I'll give my opinion on f2p girl progression. All of it is possible at VIP 0:
1. 3 starters, Jilysh, Graorpyle, Aeznell/Oronia. Just for the team bonuses or in the case of Oronia, the slightly OP ability. You have to fuse Graorpyle if you want her in a reasonable timeframe but it's one of the easier ones. But you could fill with whatever healer. And Aeznell is rng from pulls. There are honestly a few other good units that work with the starters so it's easy to build around them.
2. You start to fit in some 16 Quality, and leave replacing the starters for last. That's just because it's hard to make backline, and frontline quality is a little more important. You can make Aleina as a f2p. You probably get the Blothogone (evee girl) from black market. Well, if you ever see her you probably get her there forever since she's material for a few things. You also have the myth girls. They all seem good. The myth girls have synergy too, so if you're slow and steady enough you end up with 3 of them in a new team. They're all very solid girls but you probably don't get all 3 before you:
3. Combine Taniara. This seems to be one of the only 17 qual that you can make as a f2p. What I mean is there are a lot of limited monster requirements beyond this, which is by far the biggest f2p wall in the game. Taniara is the sheild girl 17 qual with the same OP skill as Oronia, so she'll get use for a huge amount of time. You could also make Usydora. She's an ok healer. The fact that you can f2p combine her and she's not earth shattering is probably why they let us get her as a reward in blackjack.
4. Guild battles and collo for 18 qual. Slowly. Ever so slowly. You should never buy a gem from guild points.
5. 20 qual might not even be possible right now like literally. But I think it's almost impossible for f2p without mad rng or some kind of special event to give out limited girls.
In tearms of gear:
The ash stuff is single purchase only. Plus it's called Ash so of course you want it.
But in reality you should probably spend guild points on tech bonuses. It's likely you should spend your arena points on girls for combine of 17 qual, at least the one girl for your Taniara combine, unless you're in an odd place where you try to skip them and go 16 > 18.
Ash is good but high boosted orange equipment is easier and faster.
Of course it's the same with purples. In the early game when you just have purple, you should boost before combining. Remember to boost def equipment on your frontline. When you're ready you can break these equipment down. You'll get back all the boost material to fuse.
Of course your tower points probably go to grabbing the 2 Ash accessories. But you don't have to rush those either. You can buy berries and whatever if something useful shows up.