you should upgrade your gpu, get something like gtx 970 or if you can spare some extra cash 1050 would be alot better choice since its newer.
im pretty sure the current GPU that you have is the thing that slows you down, as other components should be enough for 10man.
with that CPU 10man is what you can do basicly, maybe 12 if pushing to max, but i wouldnt advise that :P
as for Ram the common modifier for it is basicly 1gb =1char. it reaches 1gb in VERY rare cases, usually sits arround 500-800mb, but to make sure it doesint et all used up, you get 1gb. so in your case 16gb is a perfect option as you can use other things while boxing, for example youtube open etc xD
P.S if you are low on money and want something somewhat decent, gtx 960 is cheaper and will be enough for 15+ char easely.
keep in mind that you always want to have extra recources, dont try to go for bare minimum. :P