Hi , level cap is 21. to get xp + caps there are many ways, but they all depend on your character style. I know i like to hunt ennemies likes leather armored raiders south east of NCR, some people like to go north with a bunch of mercs or slaves to farm loot industrial fashion i heard of people selling spears to someone in junktown i believe, which seems like a good idea.Then when you manage to gather some decent loot, you can sell it for caps at merchants anywhere. I go to Jacob in old town Hub for energy weapons, Gunrunners for the rest...good luck
I'm surprised this link wasn't shared yet:http://www.fo2238.fodev.net/wiki/MerchantsWiki is your friend.
The best way to get loot and level fast is to go to the Boneyard and enter anywhere in the city area. You will find a lot of Junk. With 4 pieces of Junk you will be able to craft 50 BB's (press F to open Fixboy). Each time you craft 50 BB's you get 40xp so it helps you with your early levelling too.After you got like 400 or 500 BB's, go to Adytum, find Jargo, and trade the BB's for a light armor (Combat Leather Jacket or Leather Armor MK II), a gun (this dude usually has some 10mm SMGs) and some bullets.If you happen to find 10mm bullets and SMGs, go for it! most of the time the guns will be deteriorated but you can wander around the Boneyard area and try to kill Regulators in random encounters for more SMGs and 10mm rounds. They aren't very strong, but if you are low level, attack them only if there's only one or two Regulators in that enc.If you have a relatively good Small Guns skill (around 100) try to kill the 50 hp Deathclaws in the Warehouse. You can kill one with only one burst of your 10mm SMG and they give you 250 xp each. I have a character with only 90hp who can easily kill them with a crappy Shotgun.