Hanging on to the Crystals is generally a good plan at any stage of the game. But don't hang on to so many that you can't do your planned daily farms. At your stage of the game, you should be spending 50 to 150 crystals per day on energy refreshes. (One cantina & one Regular, or just Regular, one or two doses, would all be fine ways to divvy up your crystals income.)
Your Galactic War tokens have to be saved for now - your first priority for GWTokens is ships, and they don't sell ships in the GW store until level 60 (unless I have misremembered, tell me if they appear before level 60)
The Guild Store doesn't have any gear in it worth your Tokens yet. If you want gear there, you'll have to wait, but since there are characters there you need, I would start spending on Shards of characters right now. NO GEAR.
Cantina & Arena tokens should be spent, not saved, at this point in the game. So you'll need character farming plans for those last 3 stores (Guild, Cantina, & Arena.)
Are you sure yet what you want out of those stores? Or would you like help coming up with a plan for them?
Mod strategy will be another post, but sell anything that isn't a 5-dot mod UNLESS it's a gold mod, with 3 or 4 dots, and it has a speed secondary. (Even those you'll sell eventually, but in the early game those are still useful)
So level up all your gold mods that have speed, even the 3-dot & 4-dot ones. Otherwise, stick to the 5-dot mods.
On 5-dot mods, sell ALL of them that are white. For the rest, only upgrade them if they have a Speed secondary already showing, but don't sell them yet if they don't. I'll share some more complicated ways of thinking about which mods to sell & keep later, but for now, those ones that don't have speed secondaries, but aren't white either, you'll be saving those for a bit. It's not good to use money on them now, but they may turn out to be good later.
