You have very few good units, but that's okay since you're probably just starting with BF... I think you used to play bf few years ago and now you came back... There are units you own that are just too old to be useful, shion is one of those units... U need to get meta units asap or you will be stuck... U should invest in and upgrade these units
Inoko
Charlie
Vanilla
Saskya (for now)
Kirke
Gwenevere (for now)
Osiris
Sae
I strongly recommend going for RC... I see u are at RC1 rn... With those units you won't have any problems getting up to like RC6-7 and that will be very efficient later on
Go for normal quest and clear a lot of it... Get gems, summon in the main gate... Those rates are great and soon you will be unstoppable...
In the Vortex go for past festivals or whatever they are called... Those are mainly easy to deal with and there are gems hidden everywhere...
Don't try clearing BF2 stuff, or those Egypt gods levels... You won't have a chance...
Your main goal now is getting units... The thing is, the quest levels are so easy, you can basically clear most of it using one omni unit... So go for inoko, inoko, Charlie and focus on getting gems and summoning...
If you are having troubles with unit slots, you can expand it cause 60 slots is just too poor... Don't invest in it too much! I am level 920 or something like that and I have 400 slots and it's way more than I need... I've seen lots of people having 700-800 slots loaded with shitty units... Be efficient, focus on unit you will use... Sell unnecessary units for merits...
Merits are broken in the game... If you're smart, you can upgrade any unit to max in few moments using merits and merit shop...
Another trick... If you have a gift/present... You don't need to receive it instantly... If it's an unit like crystal or golem... Don't take it unless you need it... Wait for the right moment, pick it up and use it... All I want to say is that you don't want your units slots to be filled with upgrade material...