Just in case you get a 8-9 speed wheel that comes with a cassette
You can literally use that cassette with your 7 speed shifters.
Yes, it shouldn't work since the cogs are spaced differently, but it works reasonable well until you actually install your 7 speed cassette.
I think it works because of that side to side play that is built into most derailleurs.I forget the term for this intentional slop, but it is important.
Yes, there will be some gears that will be too noisy, and will slip/change/slip change- but it will be much less annoying that you would think.
I currently use a 8 speed XTR cassette-with one cog removed-with my 7 speed indexed twist shifters-shimano- on a Trek 730-roughly 1994. I do it because I wanted to use the 34 t cog of the old XTR, not the 30 t the 7 speed cassette came with.The 700c wheel is for 7 speeds-can't take 8 or 9 cassettes.
I ride intervals up and down the river levee, so I need low gearing.
Shouldn't work, but it does-strictly a cheapout-I would rather have a 13/34 7 speed cassette, but $$-$30- is short.