Yes 20 hours per week during term and 40 hours per week during vacation. Make sure you avail a vacation letter before you take on 40 hours of full time work.
No there is nothing hidden however there are detailed all their requirements on their Published guidance which can be downloaded and referred from UKVI official website.
NO. It is illegal to work on a visitor visa.
Well! There are over 1000 plus Masters degree offered overseas. It depends what course you would like to study? Have a study abroad query email info@gleamrecruits.com