I hope that you have read all the threads on doing this, I think that you will find that the immobiliser transponder pellet is a "once use only" as far as programing is concerned - and I'd think that all ebay ones are second hand (I've bought two so need to buy in new transponders). One of the threads on this forum will point you in the direction of a place that sell new transponders and they are not expensive.
The remote locking part - you would need to check if this is compatible - but you can do that before doing any more work on the key.
BTW, the Chill seems to have been supplied new with one "remote" key and one "normal" key - same as many other Seats of that period.
I've just noticed your earlier thread on this
problem - yes I've seen "just get your locksmith to cut it" - but have guessed that it would not be that straight forward for most of use. BTW, I once had a second hand VX Cav GSI 4X4 and wanted to get a second key - dealer cut one and it was rubbish - I then asked for the better solution - ie send away for a new one - result was a perfect fit key - I'd agree with your dealer, that is the best if not the only way to get a good key that does not cause damage to your locks. Even Ford dealers tend to work only from lock numbers and not just copying (worn) keys as that does tend to lead to other problems -been there done that - and refurbished many Ford door locks.