[eluser]Krzemo[/eluser]
Quote:I am not a techie (...)
From more biz POV...
I'm not sure how not techie you are not, but as you already know what to do more less, it would now best to hire someone and have a chance to have it solved ('workarounded', even temporarily) within one day and save your business

Additionally you might also learn if you application will stand the change you mention without smaller or bigger redesign (and redevelopment).
There is one thing sure - if its going to grow it will need constant maintenance...
Regs
K.
PS.
I'm not sure if it was mentioned already, but besides DB optimization - going for i.e. lighttpd and xcache gives sssserious boost.