Nothing wrong with the A5.
But if you consider an A5 you should look at the X7, and if you consider the X7 then look at the X7 Phenom.
However there is a real abundance of markers/guns to choose from. The best thing is to either find your way to one of the paintball retailers warehouse shops, or to a walk on at a local site and check out what other people are using.
Then go through the classifieds on here and on UKScenario (see the calendar link below and work on from there)
For tournament style play you want a reasonable 'bling flinger', for woodland or scenario the world is your oyster - general paintball gun, so called woodland gun, or bling flinger
First though the most important thing is a set of goggles. I4s are very good, but dont have full face cover for big heads.
As you've just had your first game you may not know the variety of paintball out there.
See some info here:
http://p8ntballer-forums.com/threads/what-paintball-costs.153010/#post-1376027
On the law of averages, unless an existing paintballer buddy took you out then you probbaly played 'punter paintball'
(Standard paintball for the masses)
Next up is usually 'walkon paintball'
The best sites seperate own gunner walkons from punters, and a walkon usually takes place once a month.
Beyond walkons, you then look to more special events, such as tournament play (which this site is mostly based around) and scenario play (see also
http://www.ukscenario.com/forum/viewtopic.php?f=4&t=34182 for the 2013 calendar of scenario events)
Tournament play is competititve, in teams, usually in an open field with inflatable cover.
Scenario play is mostly on established woodland sites, but in the last couple of years has gone indoors for CQB, in deep underground tunnels and current British army FIBUA/FISH training villages