1. My 7 speed freewheel failed and come apart, so the thread is stuck on the hub while the cogs have come off. Is it possible to remove it or do I need to use a new hub and lace the wheel again.

2. I have a spare hub but it is 130 mm rather than 135 mm. can I use the nuts of the old hub which are over 2+mm thicker to make it into a 135mm?

3. The hub is a 8/9 speed cassette compatible. I was thinking to make it into a 8 speed. I have a 8 speed cassette, rear derailleur, and shifters. Do i need to change the front derailleur, cranks and chain or can i get away with using the old ones?

thanks in advance

Did the part where the removal tool fits come off with the cogs? If not the just use a tool and remove it. Otherwise you could probably (after removing the cogs and stuff and getting to the freewheel body) clamp it in a bench vise and remove that way also

Probably not, You probably won't have enough axle length after adding all that extra spacing, maybe if you replace the axle and the locknuts...

They should work fine with the 8spd. But I would replace the chain with the newer cassette.

If it's already broken it won't matter much if it gets more broken - so, sure. Easiest is if the required freewheel puller still engages, in which case you just have to muscle it off. If the puller won't engage, disassemble with force until you reach something that can be clamped enough to unscrew the remainder. I'd recommend a big pipe wrench for the job. If you're handy with the angle grinder you can cut it off. Some skill required as not to mess up the threads.

There are a coule of different threads out there, so they might not fit the axle. But yes, in general a 130 mm hub can be made to fit a 135 mm dropout by adding spacers. You need to monitor wheel centering/dish though. Best result is to add spacers to the left(non-drive side) and then redish slightly.

You can probably get away with using even the old RD, while the front bits can remain the same, I'd recommend a chain swap though.