Hi, welcome to the forum
Buying bitcoins: any reputable exchange will require some form of account validation to prove your identity/address i.e. scans of utility bill &/or drivers licence/passport etc. I’m not sure about ‘linking’ of bank accounts, but in the case of Bitstamp for example, once you have verified your account you would then need to arrange a wire transfer, as you would do any other, with the account details they provide. I’ve done this without issue, and via 3rd payment processors such as OKPay, again without any problems.
If you’re not comfortable in divulging any personal info, then you may want to consider https://localbitcoins.com/ I haven’t used it but it is popular and depending on your location, will probably be able to connect you with a vendor willing to accept paypal. You may be paying over the odds for the privilege however; paypal and bitcoin are not happy bedfellows!
Mining: you’ll be able to find better high level summaries re mining and hardware requirements online than I could offer, but in short, it depends on the coin and it’s state of maturity. You could’ve used any old machine to mine Bitcoin immediately following its release, but as the ‘difficulty’ increases, so too does the demand on the hardware to perform calculations. Hence in the case of Bitcoin, the mining hardware has evolved from your average home computer, to high-end gaming machines, to machines designed specifically to mine bitcoin and do nothing but.
With technology evolving as it does generally, old machines always seem to take ages to do anything (especially if running Windows), so I wouldn’t recommend using one by way of experimentation; you may find the whole experience too frustrating!
Better to learn about the cryptocoins generally, identify which you’re interested in (GoldCoin, obviously....!) and then understand the mining requirements relative to the coin.
Hope this helps, I’ll send a few GLD your way so you can appreciate again how the GoldCoin client doesn’t run like a Doge.
Sent on the move