Originally Posted by Iride01

3x or 2x front?

2x shouldn't be much of a problem. Just change shifters and rear DR along with figuring out if you can put a 11 speed cassette and freehub on that wheel. You don't necessarily have to change out the crankset. 9 speed crankset and rings will work. At most you might, I say again, might see some slower or poor shifting in the front. Possibly your front DR won't have the same pull as the 11 speed shifters you get. However you can just change the rear shifter and that will be even less expensive. Might look and feel odd.

If front shifting does become and issue, you can change crankset and front DR at some point later. Of course it depends on how often you use the front DR and how critical it's shifting is for your riding.

3x started disappearing on 11 speed bikes, partly because of the choice of gearing on the rear made them not as needed, but I wonder if it was also that 3x didn't work as well on some combinations of frame design and geometries.

Tiagra 10 speed isn't a bad group either. So you can be even less expensive going to it. However Shimano 105 5800 or better is a very nice shifting group. Pair with Shimano freehub and it's very silent when coasting. At least mine is!