I want to fly from Tashkent to Taipei. I was looking at Uzbekistan Airways arriving in ICN T1 at 8:40, then either China Airlines departing T2 at 12:30 or Eva Air departing T1 at 11:40. Check-in baggage in included in fare, but I haven't decided if I will do that.

1) China Airlines gives extra transfer time BUT is a different terminal, while Eva is a bit shorter (not too short, is it?) but in the same terminal. Do I need to go through immigration no matter what, or only if changing terminals?

2) if I decide to check luggage, is this enough transfer time?

3) if I don't check luggage on the TAS-ICN leg (because I suspect Uzbekistan Airways is less strict about backpacks and gives 1kg extra weight anyway haha), but DO want to check luggage on the ICN-TPE leg, then I would definitely have to go through immigration and go to check-in counter, or would I not have to if flying Eva from the same terminal? Alternately, can I obliviously just transfer with my carry-on backpack and let the second airline decide at the gate if I need to gate-check?

4) Finally: it would cost $100 more to do this as a single ticket on Air China, which I've never taken and only heard bad things. Any thoughts on that?

Thank you!