whatever suits
We have a Bessacar E370 based on a 1999 Fiat Ducato medium wheelbase, 5.25 meters long. Incredibly clever layout and we never fill the storage, bikes on the back and five weeks in France no problem. One thing helps, we came to motor-homing from sailing and believe me, if you think a motor-home is tight for space try a 27 foot yacht. We have everything needed habitation wise and rarely spend more than three nights on camp sites in a month. Books not TV, bikes on the back, a good selection of large scale maps for the area we are heading too (obtainable from all good charity shops with patience) to supplement the satnav and off we go.
She is getting a little old at 1999 and you need to keep on top of minor issues, usually old water pipes (the van not me) ancillaries and the like but she is a simple vehicle. Mechanical injection, no engine management and by now I know my way around the fridge, heating, shower etc.
This suits us perfectly and despite looking I have yet to find anything worth the extra investment.
However.....
It may not suit you, the man next door, the guy you meet on the aire.
Define your minimum needs realistically and stick to them then just give it a go. Camper-vanning is an adventure and depends on taking your own decisions, in the end it really is up to you.....