Hi Peter B
I'm not familiar with the Paterson Orbital. I use the Stearman Press tank. It allows for easy loading of 4 sheets of 4x5. The parts come apart easily for cleaning. If you follow the manufacturer's instructions the tank does not leak. I agitate by 5 slow (ish) twist inversions every minute. Development time, for the only films I use, are 11 minutes for FP4 and 15 minutes HP5 at 20 degrees C. I rate the film at half the box speed and that seems about right for me.
The pre-mixed chemicals, part A and part B are available, also as a kit, if you are in the UK, from Nik and Trick:
Pyrocat-HD Film Developing Set is the perfect chemistry bundle for your film developing needs. Save 10% on this curated set!
ntphotoworks.com
I'm told that there is no issue using Ilford rapid fixer.
The Bellini mixes are much easier to use than 510 Pyro. A great developer but it is very viscous so more difficult to dispense and it stains anything it touches horribly. In order to retain some marital peace since I don't have a dedicated space in my home and use our utility room, I stopped using this mainly because of the stains which are almost impossible to clean if allowed to dry.
I mix, using a 5ml syringe, one shot, 5ml of part A, 5ml part B and top up to 500ml. The Stearman Press uses 485ml. We're lucky to have very good water so I mix with tap water and don't bother with a last rinse with photo-flow. If you have "bad" water I'd suggest mixing with de-ionised water.
Ian Barber has good instructions here:
https://www.pyrocathd.5x4.co.uk/pyrocat-hd-development-times/
Hope this helps
All best, Vincent