Ho Josh, welcome to Fiat 126 UK,
and please just ignore any negative comments, everybody is entitled to their opinion and this is an open forum.
the starter problem could be a loose electrical connector on the starter itself as this is common issue, check them first before replacing it, the click you can hear is the starter solenoid moving,
my advice to you on modifying the car is approach it carefully, dont go ripping it all apart before knowing exactly what you are going to do with it, and then priced, sourced and obtained any parts you wil require, or you will end up with a stripped out shell and boxes of parts lying around until you get pissed off with it and buy a corsa.
start out with the simple bits, dealing properly with any rust which will always be 10 times more than you think it is, lowering it, set of alloys, front disc brakes, clean up the bodywork by ditching crappy plastic trim etc,
there is nothing to be stripped out of a 126 that actually weighs anything and tuning these tiny two pots is hideously expensive.
not only will a cage cost you about £350, it will add about 50kg and unless you are a person of restricted growth makes it even more cramped inside, you'll also lose your rear seat which is a PITA when the first thing you want to do after passing your test is cruise about with your mates.