2017 Proforma (to 2018)

This is done for 2018 in the 2017 program. Highlight the clients you want, then click the 17 -> 18 icon (see image). 

I agree, it is much to early to transfer any except those you want to run a "test" on. 

"..Does it hurt anything to transfer now (if you're not going to work on them, just get them transferred)?  Only 160 of 277 individual returns transferred for us and I don't know how to fix that."

No, it doesn't "hurt", but beware that you will need to do it again if there's a major update to fix issues.

Supposedly, those that didn't transfer produce a 'message'.  I haven't (nor will I) transfer all my clients; I will only transfer those that I want to use to do 2018 year-end projections.  And those, I renumber.  I will then transfer them again with the "normal" client number to use for actual tax prep.

OK -off my soap box

Known issues with transferring:

Locked returns (be sure you have a good backup, unlock, transfer, lock), 

Returns with "i"s in Screen 26 (either the Org's name, or the description of items donated).