Hi, I did that trip on a Transalp and it was just fine. It is all road from the UK to Goa.
Either bike would be good.
What's wrong with your old Transalp? If it is cosmetic, then that would be no problem. Indeed, an advantage.
I know a lot about this bike, so feel free to ask away, and there are plenty of others who can help too.
Hiring is not an option: just not possible to cross most national borders with a hire bike, certainly not the ones you need to.
As for lowering, no, not advisable. Possible a little bit, (seatfoam cutting is easy and effective on the TA) but anything drastic to be avoided in my experience. It throws everything out of place.
Paddling won't be necessary on this route anyhow.
Parts? Well, beyond Turkey, nothing is available for any of our bikes. Shouldn't be a big issue with a Honda though
Worse case, you wait a week and get the part DHLed. It's a small world.
Odds on, you won't break down, and you won't go offroad. That route will put *less* stress on the bike than UK use, not more. Nothing an engine likes better than sitting at 50MPH all day. Quite good for humans too!
So when are you leaving Martyn?
Around the world 2000-2004, on a 1993 Honda Transalp