The best thing to do before spending any money is
go and play. Your fine to play just by yourself as you will be allocated to a group or drag a few friends with you. Play
several time before you spend money on markers or anything else. Buy it second hand from forums or facebook from others who have never played before and then spend a fortune on kit to find out they dont like it or cant commit as much time to play as they thought.
The first thing to buy is a mask as having your own thermal lensed mask will make a massive difference to your fun on the day when it doesnt fog up like the punter masks. Also knee pads as you will be amazed at how much time you can spend kneeling down.
A tippmann 98 is a very solid starter marker and will last forever with minimal maintenance and most fields (except delta force) will let you take it and use it with other punters as that is probably what the site runs anyway. Also good starter markers are the Gog Enmey:
https://www.bzpaintball.co.uk/gog-enmey-starter-pack
Dont buy a .50 cal make sure its .68 calibreas thats the most common paintball calibre used.
If you have the money and really want to get into the sport I would recommend this:
Buy a second hand Gtek for about £300 or so
https://www.bzpaintball.co.uk/eclipse-gtek-black
Probably the best electric mid range maker on the market IMHO.
Add a Gmek frame so you can use it on normal punter days or at mechanical events.
https://www.bzpaintball.co.uk/gmek-frame-kit-black
Also if you buy a spire 260 at BZ you can get a free vio extended mask:
https://www.bzpaintball.co.uk/virtue-spire-260-loader-se-3703
Hope this essay helps