Warning - Reading posts by me in realation to pump paintball may cause you to spend a lot of money of pumps and little on paint.....
Heres a nice litte thread with a couple of questions answered:
http://p8ntballer-forums.com/threads/so-why-pump.161940/
A bit about pump conversions for autocockers:
http://p8ntballer-forums.com/threads/converting-an-autococker.156485/
The best thing to do as always is get hands on and try it.
Regarding guns the general choice are:
old school pumps that crop up in the classifieds now and again (sometimes in bulk sales)
autococker conversions - the autococker is really a pump action with a front end conversion kit fitted, so is easy to take the front end off and install a pump kit. You just need to source the right kit for the type of autocker (usually this means self importing from the US)
new pumps recently released are the Hammer 7 and Empire Sniper (These are very different in price range as below)
The Spyder Hammer 7 is a bargain at under £100
You get a pump action gun with hopper or magazine feed options and the ability to shoot first strike
The Empire Sniper at about £350 is a very nice new pump which gives a nod back to history.
The original Empire pump by Bud Orr gave birth to WGP and set the path for the autococker.
Generaly pump players use small hoppers such as 50 round hoppers, possibly loading from small 50 or 10 ball pots, and small air cylinders such as the 13ci 3000psi cylinder. This is because they go out to shoot less paint, and take advantage of less weight and the smaller profile.
But its not necessary to do so, you could use a rotor on a pump and I've often played pump with a 68ci 4500psi cylinder - that meant I only fill at the start of the day and end the day with most of my air left. Being a member of a team I would usually still carry my full quota of pots which meant I was overloaded and could hand out paint to team mates, but there have been a couple of occasions where I've found my self shooting 'streams' of pumped paint so the extra pots came in handy.
Some people play without a hopper and use a tube feed, either 'fixed' and loaded from 10 shot pots/tubes, or the pot/tube is directly attached to the gun.
Unless playing a 'stock class' game etc there is no requirement on hoppers to be smaller for pump players, standard advice on hoppers applies, you don't need the features of advanced hoppers but if you already have one then you don't have to buy a lesser hopper to play pump.
Hopper options for a pump player:
Very low capacity & very small:
Gravity feed - you may need to tip to assist gravity
Spring feed - has an element of force feed due to the spring
Low capacity & small:
50 shot gravity hopper - you may need to shake, but the movement as you pump could do this for you
Normal capacity & size:
Standard gravity hopper - you may need to shake, but the movement as you pump could do this for you
Assisted gravity hopper (e.g. Proto Primo) - you should not need to shake at all
Electric agitated hopper, but needs batteries - you don't need to shake. It will probably still work as a gravity hopper if the batteries are flat, in which case you may need to shake
Electric force fed hopper, but needs batteries. It will not feed if the batteries are flat, but you won't need to shake
Regarding shaking hoppers - you need to shake the hopper if a few balls sit at the top of the feed blocking the hoppers feed neck. The action of pumping usualy puts in a natural shake, however pumps with a very soft action may not shake enough and you could get stoppages in a gravity hopper.