Bepisman, FE6 is my favorite game in the series, My advice for you,
Roy gets more hate than he needs, he is decent early because his Rapier, and has meh-good growths. His late promotion and sword lock are issues but do not make him complete trash.
The different attributes do not make that much of a difference/are not that different, if u care about them do some more research as I do not know the exact details.
For units: use Ellen, she is one of my favorite units in the game, she has decent magic, skill, luck and res growths, middling speed, she is of of like 3 light magic users in the game (her, saul and Yoder). Even with 1 base magic she is still very potent. Also, don't let people tell u Wendy and Sophia are useless, they can actually be pretty good, if you want to use an armor knight in FE6 your choices are Bors and Wendy (I don't count Barth/Barst) Sophia can be a very potent dark magic user, most people just use Reigh/Ray. However she has pretty good growths for the most part. If you like either of their characters or designs you can use her and she will be good. you can easily bench Oujay as he is literally just a free armor slayer. For popular units you should use, Lance/Allen, Deike, Rutger, Clarine, Shanna, Sue and MILEDY!!! Miledy is one of not only the best characters but one of the best units!. I personally like to use Clarine and then Ellen or Saul (for me Ellen). FE6 does a lot of 2 of the same unit thing, with Sue and Shin, Rutger and Fir, Ellen and Saul etc. in most of these pairs both are useable with the one recruited later being basically even (Shin has more str and that kind of thing) However both are good and it is personal preference.
Chapters have been covered well above so I will not add more