First of all you need to decide what cars your going to be doing. If you have a garage and want to remap normal run of the mill "Bread and butter cars" as I call them, then you will need to look at a couple of different systems that allow you to read, modify, checksum and flash the finished product into the ECU via the OBD port. There is no one system that does all cars but three on the market will give you access to the majority of ECU communication protocols. A decent OBD scaner is a necessity as only an idiot will remap a car that may be faulty to start with. You must check them carefully first, its part of the job.

If you want to do performance cars then I would advise that you get some more specific tuning knowledge and tooling to suit such as Wideband fuel monitor and detcans as a starting point. We also often use EGT and various thermocouples too, depending on the tune in question.

An emulator only works on some systems with most modern ones being impossible to emulate, but older ones with the right equip are as easy, or easier, than most standalone systems. Please beware of people offering live maps on most modern ECU's as its impossible.

Be aware that most systems will cost you for every tune you do, prices vary for calibration decoding but expect to pay between £30 and £100 per car fro some of the bigger companies. This can be avoided once you understand the systems well enough to code in hex or 2d, but I'm presuming that right now you don't.

Once the file is done you need to buy a checksum module for your system that will allow you to checks the file back to what the ECU needs to see for it to be satisfied the file is standard and allow the car to actually run. these are ECU type dependent and expect to pay anything from £100 to £1000 depending on ECU type and its technological standing in the industry.

I cant really give you any more info until I know what you need to do as if you just want to sell other peoples remaps like my installers do then that is a totally different ballgame and much easier so the info I have just given you is allready pointless, so please clarify.