The man who can answer your questions about MF folders and meters sells folders on eBay. He specialized in refurbishing and renewing folding cameras. Very reputable. I have done biz with him a few time. He did a bellows for me on a Mamiya Six folder, and resilvered a mirror on on the rangefinder of a Mamiya Auto Six folder. His user name on eBay is Certo6. His name is Jurgen Krenckel. I don't know anyone else who may know more about old folders.
What you're asking is a tough call. Folding cameras were in decline in favor of 35mm around the time that meters started appearing. Zeiss Ikon and a couple of others built meters into their MF folders. Others slipped accessory meters into the flash shoe. In almost all cases the meters gave you a reading and you set the f-stop and shutter speed manually. With that in mind, using a handheld meter is certainly an option.
The other consideration is that the meters of that era were selenium cell (No battery) and most of those meters by now are inaccurate at best. Selenium meters that have been closeted away for the last 60 years and not exposed to the light can be fairly accurate.
Jurgen has a web site, but I don't have that right now. You can navigate to his web site from his listings on eBay if you read his listings closely.
There were more TLR cameras with meters, but again, many of those were selenium. I had a Zeiss Ikoflex that had a meter that was actually accurate. TLR were marketed much longer than folding medium format cameras, so they did make it into the CD cell (with battery) era. I think someone earlier mentioned a YashicaMat TLR, which were very good cameras. The film format for most TLRs using 120 film was 6X6, while folders came in 6X4.5, 6X6 and 6X9 commonly.
Jurgen is the guy to talk to.