It depends on which version you are playing, I am going to explain OSRS I guess, I think RS3 is a bit more dead for PKing but here is what I can help you with.

Mainly OSRS is meant for PVP but F2P works just as well, you can get around 2.5M in game (which is hard F2P) and be able too purchase a bond for 15 days of membership, not bad at all! An effective way to get some cash is to probably kill something, Hob-goblins maybe, and pick up the limpwurt roots, they are worth like 2-3K per limpwurt root.

[ Register or Signin to view external links. ] You can click on this link for a bit more information on the root.

You can also visit the Stronghold of Security to go through that and get a bonus 10K GP on starting up your account, you can make several accounts and do this and transfer the gold to your main one if you'd like.

Other ways to make money would be, flipping on the GE; for example search for an item or something that has price influxes and such, something you can get cheaper for what it is in the GE for and try and sell it for more, be it 5GP or 5K GP. Finally, you can just PK risk PKing is probably the best way to make gold, from killing people in rune to pretty much anything probably the quickest way to make some cash.

For your account build it generally depends on what you'd like to build, would you like a main PKER, meaning high combat or more of a pure. Pures are more popular as they are lower leveled (combat) to fight more people and possibly get better loot like rune and all that good stuff so it's what people like to use.

So depending on your style, you can calculate whatever and add that all up. For example if you have let's say higher melee stats, then ranged or mage you can actually level your mage up high or ranged and they can get higher while leaving your combat level be, for example I have 65atk/66 str/68 defense/72hp/46 prayer, and I am 83 combat, I have 77/54 Range and Mage and it actually doesn't effect it.

[ Register or Signin to view external links. ] Here is a combat calculator that can help you out.

I don't really PK so I can't help you with a build what so ever so either check out the /r/2007scape subreddit or just search google for OSRS PKING Pures or Main Builds and figure it out from what you would like to go from there.