I suspect that it will be hard to earn substantial credits from Thailand like the OP...
HandyMcNab: Of course a lot of credits are necessary to play competetively, but the erratic meter should not come from the free equipment. In the contrary, to my knowledge it has less stutters and such than the custom equipment, albeit a fast meter.
And, if you upgrade, you will rise in the tiers, get more difficult conditions which will result in more upgrades!
With an old computer, it will be necessary to stop all unnecessary programs, maybe close all other browser windows. It may be good to keep an eye on CPU load (task manager) and seek moments of low load. For instance, have some patience (10 secs or more) before you shoot.
Have fun!