Bits can be bought at local auto place or auto electrics place, or POLEVOLT.CO.UK
You don't need anything remotely like 70 amp relay, the pump draws 13 amps at 12 volts so as the 12v system normally runs around 13.5volts even less current(amps is drawn) than this.
28/030 wire gauge will be fine, with a 15 amp(blade) fuse NOT 40 as it will melt the wire before it even thinks about blowing.
Earth at the battery too just to be 100% certain, easy as you have to run a wire through anyway.
28/030 wire is rated at 17.5 amps continuous, and is plenty man enough.
If you get the newer thinner "THINWALL" cable get 32/020.
You need a relay holder, type A or B relay, then the rest as you say.
Use ADHESIVE LINED HEAT SHRINK, on soldered joints, don't use crimps unless you have a proper decent crimp tool(which will be about £60).
If you look behind the rear seat n/s there is a hole about 7mm on a bit of metal there ideal for the relay holder to go(nut bolt to hold).
Type A or B is just a different pin layout, so make sure you get it correct, when you push the relay reminals in the block.
for smaller orders you might be better going to VEHICLE WIRING PRODUCTS, VEHICLEPRODUCTS.CO.UK
You would be best of soldering if you can solder ok.
tabetha