As to whether it is a maxi van, my understanding of that era of vans is that there where three weight ratings, Q10, Q14, and Q18 (maxi), which denoted the payload of the van (1, 1.4, 1.8 tonne). So if yours is a maxi it should be the highest category Q18 which as I understand it equates to a GVW of 3.5 tonnes. Of course, the convertor may have uprated it to a higher GVW, but you would assume they would start with a Q18 chassis. If it has been uprated it may have stiffer springs on the front and an extra leaf on the back.
From my experience, I have a 2000 2.8 turbo diesel Hymer. The engine looks identical to yours. I have always assumed, rightly or wrongly, that the terms 2.8 TDI, idti, and TD all refer to the same turbo diesel engine with mechanical fuel injection pump, SOFIM 8140.43.
Buying parts can be tricky at times. I usually start by looking for the original part number, eg. on the shock absorbers, brake drums, whatever, which will usually confirm you have the Q18 chassis.
EPER Is very handy but can be a little confusing with all the part number changes over time.
As an aside, looking at your pictures above, I must say it is exceptionally clean for that age of van.