basically me, and I also started playing fire emblem with 7.
but yeah, fe7 is decently difficult (at least from what ive heard) compared to some other games in the franchise, but its still not that bad to start out with I think. it gives a decent tutorial and everything so you understand the basics, so thats that too.
dont spend your gold too hard as soon as lyn mode ends. you dont want to be running low on cash when the good items start appearing in shops.
dont promote too early. a common mistake beginners make is promoting their units as soon as they hit level 10 (so as soon as theyre eligible to), but dont do that. promoted units gain much less exp than non-promoted units, so unpromoted ones grow much faster. meaning you can grab more levels on the way- levels that you will likely need.
as much as I love dorcas for his memes, yeah. the only reason to ever use him is because he gets extra levels from lyn mode compared to the characters from the next story. because dorcas is really terrible.
USE HECTOR. no, seriously. if everything fails, just kick the games ass with hector, because that works. especially in the early stages of eliwood mode. actually, just use all three lords- in some chapters youre forced to bring all of them along, and if you havent grinded them, they may become more of a deadweight rather than an asset.
last but not least, sorry if youre a completionist, buddy, but you will NEVER be able to get all the units in fe7 in a single run. two of them are locked to hector mode, which you can only unlock after beating eliwood mode. oh, and there are two cases in which, depending on your decisions, levels, or whatever in the game, one of two recruitable units will spawn. the other unit that didnt spawn will not be recruitable in that run, and wont even appear anymore. you can always only get one of the two, so never both in a single run. this is fe7s way to say 'youre not recruiting everyone in a single run'.