The less add-ons you have , the better. Also you can use cleanmem program for the memory leak issues, i run 8 clients at all time on my main computer, i rarely crash at all, except in siege war ( usually crash once during siege. With 8 clients running i get 38 FPS on all of them steady.
http://www.pcwintech.com/cleanmem
I have 3 other computers with 3 clients each running all the time and they never crash but use them for crafting and processing mainly. They are older processors and video cards also. One has a Intel Q6700 quad core with 4 gigs of Ram and windows Vista 64 bits on it, another has windows 7 64 bits with AMD phenom X4 955 and 12 gigs of ram and the last one has a Intel dual core 4 gigs of ram and windows 7 64 bits.
So has you can see i have a variety of different computers and operating systems, hope it can help you a bit