1. Personally, I've kept Justinian as my Conquest Consul even with the changes.
Murad I and Subutai are very good gens because they are essentially Genghis lite, not the version with the skin.
For Challenge Conquest and Expedition, I got all 4 single-target healers: Eleanor of Aquitaine, Antonina, Adil, and Sophronius.
They're also in my teams in Territory.
Manuel's unique equipment and unit are both too far away to be of value. He is not recommended.
Khalid, Baldwin IV and Babarossa's equipment are locked behind the paid battle-passes. They are also not important. Though missions that require Balwin for the F2P version can probably be forced using your IAPs.
However, Baldwin (and maybe Manuel) have Hero Legends which are good for resources. Only invest for these resources and cannon fodder Expedition.
Not sure about Alfred given your IAP gens, but he is still valuable for a few late-stage battles involving high-HP cities. He comes with a Hero Legend as well.
Basically, anyone with a Hero Legend is only worth their weight as fodder and the rewards to be earned.
Anyone with a unique equipment that can be quickly earned (even by F2P standards without explicit grinding) should be considered.
The exception is Murad, but his active and skills are worth it.
So far, I've made serious progress without IAPs or Drums, though I do use units exceeding lvl 20. Of course, if I removed other handicaps (no Talents), I might get further. Thus, it can be argued that IAPs are not needed to go far.
However, they come with good bonuses (Edward's additional gem slot is the best, for example), the daily rewards are helpful, and they are still powerful especially for those with skins. These refer to gens who come right out of the package from the IAP shop, and not gens from Achievements or battle-pass.
Assuming you're a decent player who uses Drums, you don't really need Su or his active. Placing troops well and using the right people as shields will do the trick. One does not need a permanent slot for healers and/or economists in all battles. Thus, it makes sense that an AOE tank like Su is not a must.
Do remember that he has a HL and it comes with its reward as well as other perks.
2. The "safest" option for Epic Battle is to avoid the units deployed. This cripples the enemy.
Besides that there are a few threads about the best units for each sub-class and builds, you can read up on them. Though, it might be best to work with what you have and what you draw.
The Tang cavalry are exceptionally good because of the +1 movement per turn upon activating their skill.
Mongolian Raiders are the Woad Raiders for ranged cav.
Special units for gens with their unique equipments still cannot be ignored.
3. If the green / blue / red icons are outlined in yellow, they are simply reinforced units that can take more dmg and maybe dish out more.
You can usually see their above average HP, but Epic battles boost your enemies' statuses by default. In the case of Epic Battles, the unit's boosted statuses aren't as obvious.
For naval warfare, I still rely on Cnut and Harald. Followed by my non-specialised gens simply because of their units.
Keep at least 3 sets of lvl 2 war gears when getting lvl 3 gears. The lvl 1 and 2 gears are cheaper by one technology point, which makes a difference.
Aim to clear Epic Battles early so that you earn more per day.
Get ready for a long farming session.
