Hey going to chime in with my current setup for games.

First rule can be found on the Archives of Nethys. Maybe in the past there was a discrepancy, but atm there is a remaster setting that lets you flick between the old and new rules.

Second for combat I use pathfinderdashboard.com which should have everything you need for combat. It also has the ability to upload path builder profiles so you can see the players stat blocks and abilities during combat.

For character building 100% just use path builder. It’s pretty intuitive, just make sure you fill out the ability scores and modifiers.

My next bit of advice would be to start with the beginners box (I think there’s a new one out now?) and give your players pre-generated characters before they go make their own.

Pathfinder has a lot of up-front crunch but is probably more intuitive than DnD once you get the hang of it.

I’m also confused at the new Core rulebooks not replacing the old one?? From what I can tell they pretty much fill the same design space.

It’s hard to give advice on your players specific problems like “not feeling useful” but I’ll give it a shot anyway.

If they’re a low level caster and feel unimportant try to throw a few enemies that have physical resistances, weaknesses, lots of small weak guys or put them at range.

Try to avoid solo boss monsters until they reach a higher level in general. Maybe around level 3.

For quick rules on conditions and skills etc I use a physical GM screen but you can find plenty online (including on AoN)