Are you talking about a complete Jobo system with a processor?
 
 A jobo 2500 tank used in inversion?
 
 A Jobo tank hand rolled?
 
 A Jobo tank rolled on a motorbase?

 A Jobo Expert tank?
 
 The tank on it's own holds temp very well. No worries about that. If
you're using a processor then the processor controls temp.

 You can hand roll the tank. You can use a motorbase [I do this and think
it's the best way]. You can use the processor.

    The number of sheets depends on the tank and the number of reels. At
least for the 2500 tanks. The smallest tank will handle six sheets. The 2580
tank will handle 18 sheets with three reels. The bigger tank would handle 24
but I'm not sure how you'd rotate the big thing. The Expert tanks have thier
own limits.

 The Jobo can do anything you want. If you want to spend the money the top
of the line processors will actually automated the whole setup. Push a
button and walk away. If you want to spend the money. At the low end you
could treat it like a big inversion tank. With you manual filling and
inverting the tank. But even the smaller tanks use a lot of chemicals like
this. Using a motorbase and something like the 2551 tank is my favorite way.
Holds 12 sheets with two reels. All I have to do is put the chemicals in.

Nick

There is no possible way for film to fall out of a Combi tank provided
that the Film Carrier is properly assembled and the Film Holding Clip is
not broken.

The Combi tank Film Carrier is designed to accept either sheet film or
glass plates. Accordingly the side plates are reversible. One side has
straight grooves for glass plates and the opposite side is curved for
film. When using film the curved sides must face each other. If not film
can fall out.

The Film Holding Clip has a ratchet and the long sides must be gently
squeezed to release the ratchet. Otherwise you can break the clip and
that will let film fall out.

Have you checked your Film Carrier and Film Holding Clip?

I've tried trays, BTZS tubes, and a Unicolor drum and roller.

I've settled on trays.  I used to get scratches but I'm getting pretty
good at developing scratch-free negs

BZTS were a pain to sit there and roll in a tray of water.  My Unicolor
developed light leaks.  

For now I am only doing BW 4x5, and I do it in an ancient JOBO rotary
processor which I bought used -- it takes a lot less chemistry than the HP
Combi tanks -- (or Federal Tanks which I sold on EBay.)
Jack

I currently use a Jobo CPP-2 and a 3010 drum for 4x5 sheet
film development (up to 10 sheets at a time). Mostly Tri-X.
The Jobo system works beautifully.

It does a fine job of maintaining temperature, even as low
as 20C. In the summer when my cold water temperature is
above 20C (as is the darkroom ambient temperature) I add ice
to the upper bath. The ice has to mostly melt to get down
the the lower bath, and if the water gets too cold, the
heater brings it back up to where it should be. In winter
ice isn't needed of course.

Constant agitation is a religious issue. I find that
constant agitation and a 3010 tank results in perfect
negatives every time, and I've put thousands through the
system now. Other people find fault with it, but I'll let
them tell their side ;-)

One warning - do NOT put photoflow or a similar wetting
agent in the Jobo processor (the lift) or the tanks. You'll
never get it out again, and will forever have suds in all
your processing. It doesn't hurt anything really, but it is
quite annoying. Everything else, from developer to washing,
can be accomplished in the Jobo. Just do the final wetting
agent in a tray and you'll be fine.

I did try development for 8x10.
Even with the soft emulsion of Forte films, scratching was not a
problem.
It works.
I use jobo and avoided HP.
It's far more consistent than tanks.
But with fresh developer you get more of the fresh look than with other
methods.
I like it best with "day old" developer.  Smoother tones and still good
detail.
I hand-roll the tank.
Just subtract 15% of the time & you're in business.