There will be enough for Linux OpenVZ PostgreSQL and PHP,...
The question put is not correct, of course virtualization OpenVZ sufficient to PostgreSQL and PHP, the issue is sufficiently fast and stable server will work under your load. And it is rather necessary to find out in practice. If you there is nothing criminal (for load), then surely everything will be OK.
And whether strongly it is most difficult to deploy all there to work, and that you may need?
Grab a VPS somewhere for a trial period or simply very cheap for a few days, try it, turn on adjust. Without experience can be very long to mess around and accidentally screw it up. If the project is rather capricious and a few hours offline means a loss, then definitely look for a admin and let he is engaged on the business server.