Hello Chris, welcome to v3m
I can't answer all of your questions, but I'm sure someone else will later on. Maybe one of the moderators could create a sticky FAQ thread, as a number of these questions crop up quite often.
The 340 came with a choice of 1.4 or 1.7 Renault engines. The 360 had a 2.0 Volvo lump, along with a stronger drive train. Most have 5 speed manual boxes, although there were also 4 speed and CVT models.
They are, on the whole, reliable cars. Most problems are well documented and generally not too horrific. Rust is the killer. The 300s are not in the same league as the Swedish Volvos of the time regarding tin worm resistance. However, a number of parts are
still available.
I don't know about the saloon, but in the hatch the back seat will fold down. It can be removed entirely without too much difficulty; the seat just clips on and the back rest is held by screws. I can just fit my bike in the back of my hatch with the seat folded down, although it is easier with the bike's front wheel removed.
My old 1.4 was good for up to 50mpg on the motorway, a 1.7 may give about 35mpg around town. Mine currently has carb issues and is giving less than 30mpg
Parts are becoming an issue. Volvo are cutting back on the ones they supply, although there is a lot of work being done to ensure continued availability of the important bits. For example, someone here is producing replacements for out-of-stock gaskets.
Load carrying ability is great for a car of its size. I've had a stack of gear piled up after a gig and people haven't believed that it would all fit in the 340 - they've come out to watch me load and been amazed when it's all gone in.
The 300 certainly has character and they are very nice little cars to own. As far as I know,
this one is still for sale and looks very nice.
[edit]Sorry, hadn't seen Tourinki's reply[/edit]