- how much does what is underneath matter to what I choose, for sort of "technical" reasons? Depending on what sort of floor it is, are there things I just can't have?
It matters enormously. If there is concrete that would totally change your options - you need to think about membranes etc. Just pull up a corner of the carpet and have a look (you can put it down again straight away and no-one will know!). In an extension, a concrete floor isn't entirely unlikely.
Think about what you put underneath it too. It's worth paying a bit extra to get insulating ecofriendly underlay (often only available online rather than instore) as this will cut down your heating bills considerably for very little extra cost!
- is the dining room laminate now going to look atrocious if I get proper wood? I don't want to actively choose and pay for laminate over wood but I'm not sure I can afford to do the whole lot right now
Are the rooms separated by a door or open plan? If open plan, it may look horrible. If separated, you might be able to do one then the other and get away with it! It is worth thinking about colour of finish and batches of wood, though.
- how do you look after wood? Is it fragile? Am I going to get into battles with the cleaner over it, or does everyone basically know what to do (except me)?
It depends enormously what you get. First of all, what kind of wood you buy - bamboo is tough as nails and stuff will bounce off it, other kinds are less resilient. Secondly, whether you go for solid or engineered. If you want anything really hot in the room in future, e.g. a fire or stove, then go for engineered as more stable. You want a decent thickness of top veneer so you can sand back should you want to.
Then there are the finishes (these go on top of the wood). I have oiled wood, which looks gorgeous but is a complete PITA to keep clean. You can get much more resilient and wipeable finishes, but whatever you have, you shouldn't let fluid sit on it for any time.
- is it a really stupid idea to think of laying it ourselves?
Depends a LOT how good you are at DIY. It's not an easy job. And you could end up paying a lot for wasted wood if you get it wrong (because it could take you into having to buy extra packs, which are expensive).
- how much does it cost to lay, relative to get?
Depends where you are. It's worth checking out quotes from a joiner because some of the stores will rip you off with fitting costs. My large, open plan lounge/dining room cost about £600 to lay in total, and they are both quite big rooms. It took a professional joiner about 3 days.
I also bought the flooring in the run up to Christmas from a horrible factory place called Floors2Go (it is a lovely product, just sold by a horrible outlet). I kept uming and ahing over the price for weeks (not deliberately, just because I wasn't sure what I was doing) and in the end I got about £800 off the original quote. And I am no natural born haggler! I think the time of year was significant - I suspect people get their asses into gear after Christmas and the deals may not be as good. But this is pure speculation on my part.