I hope you enjoy the bike, I thought the IX FS I had was one of the nicest rides. Alloy frame, I believe.

If you want to pull the cassette off and fiddle with the drive train it's almost certainly worth while scoring a cassette removal socket and a crank extractor from Ebay as your first expense, if you can't borrow them. You'll save the price of having a dealer do it.

The final gearing you end up with has to cope with uphills, downhills, headwinds and possibly, mud. Ride the bike for a week to find out what you can manage, and whether you really want to limit the bike to one gear, espeically if you travel with it. Not everywhere is flat, and one day you might want to carry luggage. Sometimes, the dreams are better than the reality.

I don't know whether the cassette is Shimano compat. but someone here will . If the bike has been neglected and you have a crank extractor, it's worth a check of the bottom bracket lube if it's not a sealed unit. Wheel bearings too, the IX FS had Quando hubs and nice rims, which are worth preserving. I don't know what's on the VIII.

The IX Zoom forks were also disk brake compat. I don't if the VIII's are. It's not a cheap opiton.

If you're going SS another weight saver is to replace the rear sus with a solid link.

If you pull the rear V brake off, keep the bits; the rear brake aids shorter braking distances, which aids performance. If you go off-road in the future the rear is useful for tight skiddy turns and going UP muddy hills. It is also a stability aid.

The Acera is Shimmy's budget dérailleur and would have replaced what was perhaps a Ju-JU original. A used cassette and cog-swapper might not fetch a lot, but could pay for the crank extractor. I have just fitted an Acera der. on my MTB, and it works well.

If you pull off the dérailleur and go SS you might need a chain tool to shorten the er, chain.

There's a monster Downtube thread on here and a lot of help in it.

Enjoy!