How to handle high concurrent users and best server configuration

Hello guys! Our community has around 600 paid members but right now we want to open a "free trial" and hope to scale to 10.000 total members in a couple of weeks and also there will be maybe 5% concurrent users at most I guess (500 concurrent users).

So I would like to hear from community owners that have similar numbers (10k or more users) and how are they handling server/hosting and any advice that you please can share

Thanks a lot!