Hi Nick,
I am doing exactly the job you are about to do!
I bought myself a Clarke Pro 90 Gas MIG welder, after reading some good advice on a welding forum. Cost about £130, and good enough for what I need to do, which is keep my van on the road - not doing a full restro, but want to either go back and fix stuff properly that I did years ago, or nip patches of rust/holes in the bud before the winter salting starts. I had a Handymate I bought from Halfords about 10 years ago - gasless. Thsi new welder is SO much easier to use, but I am still very much a beginner!!
I have bought a few panels, and used sheet for the rest. Got the sheet from the place I got the welder from - B&Q also sell smallish sheets of 1mm steel if you can;t find a local fabricator.
I bought 2 seat-belt mount repair panels. I then had to weld in a strip along the inner edge of the wheel arch - the flat bit. Went in ok. Also need to do the 'corner' where the wheel arch drops down and meets the cab floor, and I have used folded sheet for that, although you can get panels. I opted not to get these, as I only needed about 20% of the metal. I have decided to do a few patches on the cab floor itself, but again opted out of buying a repair panel, as it is only very small areas that need doing. Means I may lose some portions of the lozenge shaped pressings, but only the very ends of one or two. I'll never sell my van so not massively precious about using pre-pressed repair panels, although in some cases I can see the advantage. I was put off after looking at a few arch mouldings that you can buy from most retailers - everyone was different, so have decided to patch my good german metal rather than replace all. I will, however, use a new 'inner' step repair panel, as mine have long gone - in fact I don't think I ever saw them!
I have taken some pictures - I'll post some, with the usual cavitar (sp!) that I am a beginner welder!!! It isn't prefect (although it has cleaned up ok) and I know some of the work done by guys posting here with more patience than I, is far superior! Everyone has different circumstances - be it time, garage space, finances, skills or patience.