Asperius wrote...
1- Does DA 2 models (elf and qunari) have any problem with DA:O animations?

qunari shape is very similar between DAO and DA2 so the animations work pretty well. DA2 elf shape is... well, it's what it is, so if trasferred intact it'd have the same animation issues elves have in DA2 (waddling like the "i'm not drunk officer i swear" ducks, and whatnot)
2- Does DA:O support "scale with level" system of DA 2?
DAO has the material scaling system -- if you put an item in chest or sell it to vendor, the item's material (and consequently the base stats) are adjusted to player's level when the zone is loaded. It doesn't include scaling item bonuses.
3- Is it viable to mark companions according to romance or personal quest completion?
If you mean DAO there's flags which indicate whether companion had sex with the player and what stage of relationship they're currently at (warm, friend, maxed out) Companion quests typically have their own flags as well although i'm not sure if these are transferred to Awakening saves and onward.
4- How hard to apply DA 2 human armors to DA:O elves? (Does a simple rescale works?)
Not a simple rescale since unlike what people tend to say the outlines of elves and humans in DAO aren't actually identical (the humans are stockier without making elves look terminally malnourished like DA2 did) but yes, it can be done as the picture shows.