Well - owning a 147 JTDm and having driven a 1.6TS of my uncle, I can give you my view of a few things. The 1.6 is a nice engine - at least when you keep it above 3k rpm. This is not very positive for fuel-consumption - but as with most petrol engines - revving it is fun :P
That said - I wouldn't go for the 17" on the 147. There are 2 issues. First is the rear suspension. Unless you change it - it will touch the chassis on a lot of bumps if you transport ppl in the back. Second is fuel consumption which skyrockets. Friend of mine switched from 16" to 17" and his fuel-consumption raised noticably.
Regarding your other questions - as norbert already said - all 1.6's are TS
The JTD engines are very tunable, but go to a tuner with a good reputation... In the UK, angel tuning
seems to be 'the standard'. Don't go for cheap & unreliable tuning like e.g. powerboxes - avoid those at all costs
I think all models have AC, only the cheapest cheapest model here I could get w/o. There is a standard 'alarm' system which has been approved by the european insurance companies, but a more sophisticated system is optional. The interior indeed feels good
Lowering the 147 is done quite a lot, since the standard setup it's rather high. I also prefer standard Alfa Alloy, most of them are beautiful
Would also avoid bodykits, though I've seen some very nice and not too flashy ones, but those are usually rather expensive, I'd give this money for a better engine/model/well looked-after-one as norbert also says...
Oh yes - if you go for a used-one - check the service records and standard stuff, cambelt changes, ... This is rather important for an Alfa