Change Old Site from Single to Multisite

I kind of know the answer to this question, and have searched a little for this, and have read a bit about it all in the past, but just wanted to ask again to be sure – especially now that we using wpmudev servers . . .

Can I change an old existing single-install website over to multisite?

I believe the answer is yes – and I know that I will have to watch the URLs (using subdirectories) and plugins. Is there anything else major I should do before making the transition? Are there any other dangers?

We have two sites that have been in existence since 1999. They are community type sites with an individual page for each business in the community. Both sites are now on wpmudev servers. Their themes are currently being updated to something new since they were custom made and no longer compatible. Once the new themes are complete, we want convert them to multisite(s) so that all of our local clients can access their own home pages and make changes, etc. We think multisite is a good way to make this happen.

Thanks for any additional advice you might have here. We are still very new to multisite but feel much more confident using wpmudev servers.

– Cat