Is it possible to install multi-db on a multisite with a few hundred existing sites

Hi,
Two questions:
I have recently installed wordpress multisite. I am not using multi-db yet as I am not sure how popular the site is going to be, but I was wondering, if in the event should i need to upscale, is it possible to install multi-db on a multisite with a few hundred website already in existence?

Second question: Where would I find someone to install multi-db for me?

Thanks for your time.