These games are an old favorite of mine they are great games that took if you take the time you can get a lot done. My advice for the game is as follow spoilers are included:
look for a guild your gonna need it for a side quest, digimon evolutions and, item locations
the games do not share all of the same locations so just like pokemon you will have to get both versions and trade like crazy. you can also make digi-eggs but issue is that you can only hold up to 40 digimon total.
Locations also vary as well if the link up is like this
task canyon (dawn exclusive)
magnet mines (dusk exclusive)
pocess factory (dusk exclusive)
you can access "highlight heaven" in both games the issue is that in order to do it in dusk version you need to do it through side quest. Those quests are locked behind side quest missions that you need digimon with particular personalities in your farm to get access to those mission.This is for many areas in both games outside of the main plot.
the difficulty if any does also depend on the game. Both games use completely different layouts for each game. Do not expect it to be easy in one game over the other. Both will give you the same level of difficulty when it comes to overall playablitiy. Note Dawn map layout for many areas they share in comment are easier to traverse especially the halfway point and final dungeon for plot reasons.
other then that I would recommend them still for the amazing line up of experience they can give to fans of the series and people looking for a change up from your run of the mill RPG, monster catching games.