It's not essential for you to have your own marker, you will most likely be able to rent gear from the site which saves you shelling out £200 unless you intend to keep on playing
What sort of game is being played? Using their own would point towards a walkon, but people do sometimes take their own to punter games
The most important item is a decent set of goggles
Wear comfortable casual clothes and footwear. Preferably some fingerless gloves and a scarf / shemagh etc
Then add gun, hopper, air or co2 cylinder (depending on what fills are available from the site)
To go with those you need pods and a pod belt to carry your paint
On the day you need paint. Buy from the site
If going on a punter day then all gear is inclusive, if going to a walkon then the gear can usually be rented for about £5
The Omega is fine and has a basic hopper in the sale thread mentioned above.
However a rental marker would be approximately equivalent
What sort of markers do the guys at work have?
If they are electric bling flingers you would find yourself outgunned. But that is also dependant on whether your work mates are dicks and pick on you, or if you 'out tactic' them