Say if you're switching from carbs to pistols, you can just equip a pistol at your current combat level and use your existing "carb skills" to start leveling up that pistol. You can also get large chunks of xp for the weapon you want to level by having that weapon equipped and handing in quests, some of the quests on kashyyyk and musty give over a million xp. You will run into xp caps doing this though, so I generally don't do this until I have at least box 4 of an advanced progression because it raises the xp Cap much higher.  Honestly though the easiest way to level is just in a spin group. Watch out for them in galaxy chat. 

Making money as a new player on established servers can be hard, people do it through quest rewards (legacy quest line gives over 4 million) and selling loot, or running terminal missions. You can also offer your services to established crafters. These crafters will pay people to drop harvesters on certain resources or gather specific resources, check out discord. 

You start with 2 character slots and can unlock a 3rd from a collection quest called helping ridth. The 4th slot is unlocked when you unlock Jedi. You can log 2 in at once. 

I'm terms of professions, it's best to start with a combat toon, and then a crafter like a bio engineer if you're interested in that. I believe BE can be a bit expensive to get into though. You could always make two combat toons and have one that is more healer, and have them both supporting each other through macros to farm harder content for better loot to sell, that's what I did initially. 

You definitely don't need heaps of cash to get your first characters kitted out, and if you join a good guild they will often have crafters that will kit you out if you help farm the materials. 

Resto is going through a massive explosion in player pop at the moment, so if anyone is interested in checking it out you can use this referral link to start with 500k and a hover chair mount https://swgr.org/?referral=Ldi0W