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.

Since Dark Link covered 1 and 2 pretty nicely (I consistently have a full inventory at 125 max ), I'll say what I can about 3.

Lorand is pretty old, so he's not as useful as he used to be. I'd keep him on the sidelines.

Ramna's main use is pretty niche, but aside from that, she's a fine unit.

Reeze and Golem are a bit old as well, but they're still decent. Reeze is one of the few units with the Status Nullification Leader Skill, so she has that going for her. Golem hits like a truck, but his Brave Burst gauge takes a LONG time to fill. I wouldn't use him, honestly.

Azael, Orwen and Lucina are all solid units. Level them up.

Aside from that...

Save up your Honor Points for Honor Summon events, which Gumi will roll out every now and then. Expand your unit space and inventory as you please (this item guide isn't 100% comprehensive, but covers a lot of the items you will encounter). Oh, and log in everyday, since you will hit a point where you have a chance to get a free Gem each day.

Added!