Not sure how much room you have to play with but you need as much space as you can get. I did mine when I changed the manifolds so it was dead easy, lots of room.
I'm an advocate of Epoxy Mastic
http://www.rust.co.uk/epoxy-mastic-rust-proofing-paint/c28117/ but only on certain bits, like Trailer parts or parts which you can see. Reason being, is because, it is an Epoxy Paint, it doesn't cure the same way as conventional paint by drying, it cures chemically and seals in whatever it covers, which is good. It is supposed to seal in oxidation so it can take out any oxygen and stop it. If it doesn't then oxidation takes place underneath it which might not be seen and therefore a disaster might occur as in the case of a water jacket on an engine.
Consequently I wasn't brave enough to use it on my engine so I opted for some Kurust, which is supposed to turn rusted metal ( as long as it is not flaking) into a paintable surface and then used Hammerite Smooth Black Paint.
I first tried some degreasers, 1st one was the smelly one Gunk, but that only really took off some of the muck, next was a spray type foamy one cant remember which, smelt good but was useless, then I tried Swarfega Oil & Grease Remover, but eventually went back to Paraffin which I manage to buy from Homebase in 5l plastic containers. I brushed on the Paraffin gently on all affected area's knowing that when it dried it would leave a completely grease free area and subject to rust, however when the rust did appear it was treatable.
So I treated the area with Paraffin then bought lots of cans of Brake Cleaner from Halfords and with the red tube attached cleaned off most of the grease and paraffin..........................more to come!

The bilge was easy, washing up liquid from the pound shop with a dishwashing brush attached to a piece of wood by tightly bounded electrical tape then the muck washed out with a hose through the bung hole!