Leave leeway for other processes. If you're talking a bot, get 8gb of ram for 10.
Well it depends how many processes you are running both in the background and on screen. If you have lots of browser tabs open, expect to take up a lot of ram. Similarly if you have a lot of things like steam, origin, itunes, browsers, photoshop etc all open you're going to use up even more. Go with 8 or 16gb ram to safely run around 10 bots and still be able to do other things.
just get 8gbs of ddr3 ram, is really cheap now a days, it'll be a better deal then keep upgrading your old core 2 duo setup, just get a lga 1155 setup and u are good to go while future proofing a little bit.

