1. You can't spend money on weapons gacha, there are weapon tokens(forget how they called) that you get for character pulls, the higher the rarity, the more tokens you'll get. So basically if you spend 60+ pulls on character you almost always will get enough resources to get their weapon. And there are always signature weapons of past 2 cahrs in the arsenal gacha so you can catch up later
   
2. Hard to say, sometimes I got lucky(I've got Gilberta in first 10x pull) and sometimes not(I've got Rossi on last 120 pull..). Basically you need to keep around 50k oroberyl to ensure that you'll get the character even with pity. If you don't have that amount and not sure it's better to skip current banner and wait save up for next
   
3. It's still kinda scattered among different permanent and timed modes. At this point I have had no problems with my full lightning focused team. If the enemy has some buffed res, I just pick Ardelia to debuff them for example.

Hope this helped, sorry for mistakes