If you can afford it go with the kickr core or kickr. Going 2nd hand is certainly an option, but based on your post perhaps new with warranty will suit your needs better.
The trainer can be controlled with the the wahoo app or a range of garmin devices with no additional subscription. Apps like Trainerroad or zwift are not required but if desired can be used have an additional cost subscription.
It's an expensive purchase but a great training aid.
Jhb is very underrated, and areas sround zoo lake are lovely. I ride with ICG on weekends a few times a month and agree with the comments above.
If you would like to join me for a ride sometime, ICG or generally, or just send me a direct message and I'll pass on my details and we can arrange to connect when you are here.
I think the best would be to get a 2nd frame and move the parts across. I will sponsor R500 towards that replacement frame. Whatsapp me on 0*7*2 4*3*7*1*2*5*5 to arrange.
I have a 26er medium you are welcome to use if you like. No charge, may just need a once over as hasnt been used for a bit.. Direct message me if it will help you and you want to use it.
Not saying it's not possible but I would not trust the flow as accurate power. One reasonability check is to weigh yourself accurately with your bike and cycle up a longer hill with a relatively constant grade with no wind at a steady power a few times. Compare your times with a few of the online calculators available. You wont pick up if its say 1 or 2% out but probably will pick up 10% out
