Welcome to the yard...
The T4s are popular enough now that a decent one can be more expensive to buy than they used to.
I, personally, would recommend the 2.5 over the 1.9. I like the extra power, better on the hills and I always prefer to have a bit more oomph in case you need it. The 1.9 is a simpler engine though, for maintenance, and does better MPG (so I've heard).
The LWB/ SWB decision has to be down to how to want to set it out? How many of you will be using it? Do you need a permanent space in the back for storing kit, or bikes etc.? Personally for me and the missus going away, the SWB is more than enough.
Look for a solid basic van without all the added bling and 'surf bus' in the advert title and you'll have a nice base to start from. I started with a panel van, but if I got another I'd probably start with a caravelle for some of the added spec, sound proofing and strengthening for seatbelts in the back if you needed...