First of all, I take it you've read this thread
http://www.golfgtiforum.co.uk/index.php?topic=18122.0 and the links within it and also this one
http://www.golfgtiforum.co.uk/index.php?topic=27078.0 as I suggest starting there. I'll try and answer some of you other questions too.
I've no pics, but the power hood will be the middle switch of three in the centre console in front of the gear stick. To take the hood down you need to unclip the hooks at the top left and right of the windscreen, then with the key in the ignition but ignition off, so literally put the key in the ignition and leave it. Then to take the roof down press the leccy hood button down and to put back up press the button up, dead simple honest. Just remember that the ignition shouldn't be on, it's for safety as you wouldn't want to take the hood up and down while driving.
If you are really unsure then get an AA RAC inspection done, but cabs are usually well looked after and if it's got good history or a lot of bills then you should be ok but if it doesn't feel right, walk away, there are others out there. The roof condition will be obvious to you anyway so check for rips and tears or places where the roof folds as they will go there first.
Heated seat buttons are on the dash, to the left of the steering wheel, they are a wheel type switch, the top wheel does the passenger side and the bottom wheel switch does the drivers side. They should have a dial with a heat setting of 1 - 5.
Rivage is pronounced Riv-arge, or maybe that's just me being posh.
I had a Rivage for four years, so if you need anymore info then let me know.
One thing to check is the fuel relay switch and the fuse box, the fuse box is under the kick panel of the passenger side and the fuel relay is the top left, take it out and see if it has melted the fuse box where the contacts sit in, it's a common problem and I guarantee that the fuel pump relay will cause you issues. It can be fixed short term by sandpapering the connections on the relay, but ultimately if the fuse box has started to melt then it will need replacing eventually which is what I did in the end.