You will only need a shutter if your exposure time is shorter than a few seconds. Otherwise your dark cloth will do just fine
I did this for a couple years.
As I said, you will find that nothing about large format is speedy. Long exposures in the 5-30 second ranges are not atypical. The JML lens is going cheap right now, might be worth picking up even if you don't intend to use it as a primary lens.
What kind of camera are you using or planning on using? Many of the Graflex press cameras had giant rolling curtain shutters which would open your possibilities a bit.
If movements aren't important to you then there is the Graflex RB-series, which are 3x4, 4x5 and 5x7 (rare) SLRs. The D model is kind of outrageously priced right now, but the RB Series B is running around $300 with a lens.
I owned a Model B, it's a positively epic camera to use. The lenses on them are nice, classic tessars. Not super sharp, but have that classic tessar quality to them. I'm sure SK Grimes could have something more modern (like the JML) mounted.
Using the rolling shutters in a graflex, a high tension, wide slit setting allows for handheld use down to about 1/30-1/15 sec pretty easily. My RB Series B had a maximum shutter speed of 1/1000.
