I can only speak about Ironclad and Silent. I have A20'd them, but I have only A1'd Defect. Note I have done a Heart kill yet, so strategy might have to change for that.
The answer for planning routes is.... it depends. It depends on a lot of things. But here are some general points-
Killing an Elite gives you a guaranteed Relic. You also get a card, and you have a higher chance of a Rare (yellow) or Uncommon (blue) cards. Some relics are completely game changing, and are almost win conditions on their own, and you can build your entire deck around them. For example, some of my favourites - Shuriken (+1 strength if you play three attacks in a turn), Paper Phrog (vulnerable enemies take 75% more damage instead of 50%) and Paper Krane (Weak enemies deal 40% less damage instead of 25%).
There is also a chance you will get a crap relic and a crap card.
In Act 1, I will typically go for more Elites with Ironclad. At least 2, even 3, maybe 4. This is because he can do good damage even without additional cards (bash with vulnerable) and he can heal up. Its slightly different with the Silent. Particularly at higher ascension levels. The Silent cant do enough damage without at least a few good cards, so I will make sure I fight a few monsters before I consider taking on an elite. I also avoid pathways that lead directly to an elite, and dont give me the option of taking a different direction if I didnt get lucky with the cards. Its also really useful if there is a campfire directly after the elite, just in case you need to heal up.
There are three different elites in Act 1. You need to learn what cards are good against them. The demon is just a damage race so you need hard hitting attacks. The three sentries - well you ideally need some AOE cards to take these on. Lagalluvin, he follows a very specific pattern and hits hard. but you also get a chance to attack when he pauses. He also reduces your strength and defence every four rounds. This is very dangerous - if the fight goes on long enough, some cards will do zero damage!
You dont know for sure which elite you will get. But whichever one you do get, you definitely wont get that one in the next fight.
For Act 2, it will completely depend on what cards I have. If I dont have good AOE cards (Whirlwind, Dagger Spray etc) I will avoid elites until I have cards like that. Two out of the three elites on Act 2 are three enemies.
In Act 3, I will avoid all elites. Some of them are very tough. I will only go for an Elite if I have no choice (all paths have an elite) and in that case I will go for the latest one (so my deck can be as strong as possible) and also prioritise ones near campfires, so I can heal up before/after if I need to. If I have a really, really good deck, I will go for additional elites. I do this very rarely.
My route plan for Act 1 will be: Enemies first to get some cards. Then priorities will be Elite > Campfire > Shop > Enemy/Event (depending on whether I have enough good cards to get by yet).
For Act 2, it will be Campfire > Shop > Event > Enemy > Elite. Elite will go up a few in priority if I have the right cards. I also like to hit a shop early to spend the cash I got from the boss.
For Act 3 it will be Campfire > Shop > Event > Enemy > Elite. I will also try and hit a shop as late as possible, to spend all my cash.
For campfires, my priority would normally be-
1) Really good upgrades: Some cards have an amazing upgrade. For example, Noxious Fumes, goes from 2 poison per turn, to 3 poison per turn. Thats a 50% upgrade. Thats massive. Some card upgrades are minimal. For example, some of the ones that just become "innate". If you have a small deck, you will get to that card soon anyway, so dont waste an upgrade on it. Make sure you look at the card, and it tells you what the upgrade does, you need to know what these are, and what the good ones are
2) If I have a relic that allows me to remove a card at a campfire (Toke) or increase my strength (Gira), I will normally prioritise these over upgrades.
3) I try and only heal up if i have really low health, or just before a boss. For Act 1, I can normally get by with 30 or so health for the bosses. For Act 2 and Act 3, I like to have as close to full health as possible
When spending money at the shop, removing a card is practically the top priority for me. There are only a few cards/relics that I would prioritise over this. These are Footwork, Apotheosis, Shuriken, Paper Krane, Needle and Thread, and a few more. Just by going through the game, you normally get enough cards, so theres is not normally a need to waste cash on them. However, I might buy cards in Act 1 for early damage for The SIlent, even prioritising this over card removal. I rarely, if ever, buy potions. You get plenty of these in fights. The only exception is the final shop in Act 3, when you have nothing better to spend your cash on.
Now this is the most critical point, so listen up! For me, Removal can be the most powerful upgrade in the game. There are two reasons - firstly, it completely eliminates the chance of you drawing the rubbish card you removed. I prioritise strikes. Almost every card in the game is better than a strike. Now the second reason - It increases the probability of you drawing a good card, and that can save your life. Its simple probability really. Heres an example-
Lets say you have ten cards. five defends and five strikes. You are facing an enemy that has 10 defence each round and never attacks. Each round, you have a chance of playing 1, 2 or 3 strikes. If you play 1 or 2, you dont damage the enemy. If you draw play 3, you do. Now, lets say you have removed two strikes, and replaced them with attack cards that cause 9 damage instead. Now, you have a chance of dealing 23 damage (9+9+5). You will kill the enemy much quicker. You can apply this logic equally to defence. And even more so to power cards - The fewer crap cards that are in your deck, the quicker you are likely to get your power cards in play. All of these things turn the tables in your favour. Remove those cards!
One final point - I will always try and take an energy relic from the Act 1 boss reward (or Act 2 if I didnt get one in Act 1). Energy is so, so important, and again turns the tables in your favour, as you can play more cards. I take them in this order, more or less-
Sozu (no more potions)
Ectoplasm (no more gold)
Fusion Hammer (no more upgrades at camp fires - in my opinion no amount of upgrades trumps extra energy. Plus you get some opportunities to upgrade from events)
Velvet Choker (no more than six cards per turn. This would probably be priority 1 for Ironclad, as Silent tends to have more useful zero mana cards, so plays more cards, but Ironclad rarely plays six cards in a turn)
Cursed Key (every non boss chest also gives you a curse)
DONT take the Kite one, that discards two cards per hand in exchange for 1 energy. Its completely rubbish. Unless you have a relic that gives you extra card draw per turn, then I might take it, depending on my deck.
Busted Crown, gives you two fewer card choices in return for one energy. I would often still take this, particularly if I have already have good cards, and especially if I have the relic that gives an extra card choice anyway.
Actually, one final, final point. If you ever see the "warped tongs" event, that allows you to get the warped tongs relic (upgrade a random card each turn) but gives you the curse Pain (lose HP equivalent to number of cards at the end of your hand). This can be absolutely amazing if you get the event just before, or close to a shop, as you can just remove the curse. However, Pain is really, really damaging, so be careful of taking it if a shop is too far away, or there isnt one at all! The only exception to this is if you have Tools of the Trade (draw 1 card and discard 1 card each turn). This is a Silent card, you can just discard Pain every time, until you find a shop. Im not sure if there is an equivalent tactic for Ironclad.
Fuck me, I love this game.