HI Guys,
Fair play for having a go, the best way to learn mechanics is to jump in at the deep end, have a load of bits on the drive then finally work out how it goes together. Once you have took a car completely to pieces you realise its not that complicated.
As for mig welding, don't just have a go on the car straight away, you can write off a shell by doing that. A night coarse is a good idea, its again not that hard it just takes practise to get the hang of it.
An engine swap wouldn't be that hard, don't be put off by it. A 2.0l zetec should go straight in and is more tunable than the 1.7l.
Polybushes would be a good upgrade, they will make as much of an improvement as shocks and springs.
I would heavily advise a few safety measures, fuel and battery cut off switches.
To be fair it looks like your doing well as it is and a puma is a good choice for a track car. My girlfriend used to have one, before she sold it I wanted to do the same thing to that. Best of luck guys.