well the tank will depend on a couple of things. first of all a certain UK operator doesn't allow you to even use your own tank so check that first and second if they are able to fill your tank for you. do they use co2 or HPA. hopefully it will be HPA as co2 is more or less dying out. if they cannot fill your tank do you have access to a compressor (e.g. a dive centre) that you can have your bottle filled from?
if HPA is available and you can use it then get a 68 4500 fibre wrap tank. they hold loads more air, are lighter and are much more comfortable against your shoulder.if its co2 then you can't use your own gun as electro-pneumatics (such as the etek) will be damaged by co2.
hopper depends what you mean by rules. if its a punterball site that operates for birthdays, stag do's etc then its likely they don't want your gun shooting too fast in which case you can either just use one of their gravity fed hoppers, or buy any reasonable force feed loader and change your gun settings so that the rate of fire is matching what a rental player would be able to shoot (around 8 BPS). a force feed is the better choice since you won't need to worry about shaking it to shoot and it will be consistent. best cheap force feed loader i would recommend is an invert halo too or alternatively go see if you can get a hold of a prophecy or rotor if you can afford them.