The RTR is good to get you going for the price but depending how good your driving is and how you want to compete you can upgrade a lot of things it. People upgrade the chassis to the EU and also the shocks, essentially though, to get you going you don't really need this, not until you've learnt how the 8th cars drive and can get yourself around the track. One of those "to finish first, first you must finish" things. If you upgraded the Servo's it would do you a season, if you were really hard on it or had unfortunate accidents you might need to replace stuff but that could happen with a cheap or expensive car, it's racing after all.
I'd say an Argus A52 with JP4H pipe combo for about £170 is a good bet for engine and pipe.
You can get a Gel battery for the starter box, much cheaper or use a lipo.
You can get receiver batteries cheaper than that too. I'd recommend a LIFE one though, I've seen people blowing servo's with the lipo's rx packs
On top of that look at your tools, you will need a plug spanner for removing / replacing your glow plugs. These can be bought on a combo wrench that also has the wheel but spanner on it.
Additionally you'll need
Glow Plugs
Glow Starter + Charger
After Run Oil
Fuel Bottle
Air filters / Air Filter Oil
Diff Oils
Shock Oils
Any specific tools depending on what car you buy.
I love this forum but it is mainly 10th and you will find more on Max Bashing. Have a look, the season is starting and there are deals to be had with people changing chassis's.
Losi are great, good cars, good readily available spares.
Associated again, great back up.
Agama - Fantastic - but I would say that as I own one.
JQ - going well.
Mugen - Super strong race pedigree.
Kyosho - winning championships for years.
Let us know how you get on.