I wouldn't bother trying to get Aerith's last limit break unless you want to spend A LOT of time grinding in disc 1.

The Midgar Zolom is tough to beat when you first encounter him, but its Beta Enemy Skill can make disc 1 a piece of cake. Other notable Enemy Skills available in disc 1 are White Wind and Big Guard (available from enemies around Fort Condor and Costa del Sol respectively after you get the Manipulate materia) and Trine (cast by various enemies and bosses). Enemy Skills are far superior than magic materia for most of the game.

Unless you feel a dire need to grind for levels/AP, I would advise you to wait until you get the Tiny Bronco later in disc 1. Then I believe you can reach the island of Mideel (southeast corner), and its surrounding forest is one of the best places to level up in the entire game (arguably until the final dungeon).

I would advise getting Yuffie as soon as possible, which allows you to do the Wutai sidequest after you get the Tiny Bronco. It can be fairly difficult at that time, and some people find it very annoying, but I think it's very entertaining (if a bit frustrating if you're unprepared and under-leveled). It's also worthwhile to get various items, including the Leviathan summon.