New to org.

Been using wordpress.com for a while and it seems to be working well.
Now in the process of setting up my own business and have got a ww.wp.xz.cn site hosted by 123-reg.
Struggling with 2 issues at the moment:
1. Which theme would folk recommend for a business selling sports equipment to schools…ideally it will need a Pay Pal function.
2. I can download onto my Mac, but how do you actually install it?
Thanks,
bryn