This is basically what it says on the internet:- Re-circulating cooker hoods push the air through filters, these filters then remove any cooking smells before the air isreintroduced back into your kitchen. Most modernrecirculation hoods feature a basic grease filter as well as a charcoal filter, these work together to remove grease, food smells and smoke from the air. If your air is not able to escape in to the room as above, and it's fitted somehow differently, it may possibly be incorrect, you'd need to see the whole thing. However, rinq is correct, you shouldn't have a gap underneath and maybe air is escaping somehow to where it should not be.

looking at your image, I can't see why not. It matches your appliances and white worktop, Perhaps add white glass splash back or white tiled walls?

I had the same dilemma a few months back. I had new kitchen put in along with new extractor. it was at height of 70cm above gas hob. the extractor come out 50cm. I spent a few days trying to get used to it but in the end I was not happy and got the fitters back to raise it to 90cm. it looks a lot better and reduces the risk of me banging my head off the side of the extractor!. no problems extracting steam at that height. Glad I got it done as it would have annoyed me otherwise.

No particular reason why you couldn’t do as you propose, as long as the adequate venting is provided. I am puzzled why you think canopy hoods are so expensive. You could, in fact, opt for a couple of smaller ones, have them independently operable and still not have spent a huge amount. And your Rangemaster hood will have some residual second hand value too.