A smart trainer and a bicycle will give a much better experience in Zwift than the Schwinn. There is a very short list of indoor bikes that you could consider and they’re all pretty costly compared to using a bike you already own with a smart trainer. Wahoo, Wattbike, Garmin (Tacx), and Stages are the only good indoor bike manufacturers for use with Zwift. Decent direct-drive smart trainers start at about $500.
The 800ic is a spin bike, I went the Schiwinn IC4/IC8 route at first, fully functional with Zwift and other biking sims for the first while and enjoyed it. But I enjoyed it so much I bought a Wahoo KickR V5 to get better immersion of the game and a better feel plus I wanted to race. The Schwinn will be over estimating your watts by about 100 so it will make it look like you are better than you really are.
I first bought and used the 800ic, which is a very good spin bike. But after two months of using it I upgraded to a stages Sb20 bike. And like Jason said, the output of watts is way over. I have lots more fun riding the sb20. And the 800ic is not controlled by Zwift, so you have constantly turning the resistance knob for changing the resistance…
The complication with the Scalpel will probably be getting enough resistance from the trainer with the small front chainring. In Zwift, you can’t adjust the basic level of resistance manually, so if the bike has a small chainring like 32-36 teeth then you may spin out on flat terrain. If that happens the workaround is to use the QZ app (qzfitness.com) in between the trainer and Zwift. You pair the trainer to QZ, you pair QZ to Zwift, and then you can use virtual gears in QZ to get enough resistance.
Also if the bike has SRAM 12 speed, you will also probably want to buy a SRAM XDR freehub and cassette for the trainer.
Assuming you put a new cassette on the trainer, a new cassette won’t increase chain wear compared to using it with the more worn cassette on the rear wheel. The only issue would arise if the old cassette and chains are already so worn that they don’t mate well with the new cassette.
Yes that would work better. I would get something with an 8-12 speed Shimano drivetrain and 2-3 chainrings. That way you can order the Zwift Hub with the correct cassette included. Clean the drivetrain and put a new chain on it.