Brave Frontier

Hope it's appropriate for a new like me to post this here
Just started like 2 weeks ago and not sure what my strategy should be for proceeding, since the guides that I can find through Google and Reddit are mostly either "Let's tell you all the basic stuff that was covered in the tutorials" or "We assume you're a 'pro' already so we'll talk meta and use acronyms for everything."
My questions:
1. Should I be spending all my gems on super rare summons whenever there's a rate-up event? Should I be saving them instead?
2. Does the base inventory problem (50 max) ever get fixed with leveling more or do you have to cash in to fix this? My inventory is always full.
3. What I've been doing up until now is trying to save up evolution units and fuse gods for when I actually have units worth using them on. My current options are Lorand (5), Ramna (4), Orwen (4), Reeze (4), Lucina (4), Azael (4), Golem (4). (Seems like the game wants me to do mono-fire or something ) Any of these worth keeping in the long term?

Any other free tips?

BTW, my ID is 0343266919.

Lucina is a decent lead and so is Orwen for new people. Reeze is a good leader against status inpailment. I'd use any of those 3 for long term use. (Reeze is replaceable with a premium healer or with spheres)

Also added.