Hi Marcel,
I've used the HP Combi-plan tanks a fair amount. They're fairly easy to load in a changing bag once you get the hang of it. They're also good and tight. Each one holds 6 sheets of film, but I think it's best to start out doing four at a time until you get the hang of how the film goes into the holder.

One thing I would recommend is putting the film into an already filled tank, rather than pouring the chemicals in after the film is loaded. Much less chance of streaking this way.

I started out with two tanks. I'd take the loaded film holder (inside the changing bag) into a dark room and put it into a water-filled tank for pre-soak, then go dark again for the minute or two it took to switch the holder into the tank filled with developer. Then, by the time the film was ready for fixing, I'd shut out the lights again and switch the holder into the tank full of fixer.

Never had any trouble with uneven development using this method, and I wasn't confined at all while doing it.

Now that I have a darkroom, I still use them unless I'm stand processing, and for that I use an ancient (monster) Morse unit that's six or eight tanks in a water bath.

Good Luck!