Go with MS-I, that way you can run MegaSquirt'n'Spark-Extra, which has more features then MSII.
You can make the harness pretty easily.
You tune MS with a laptop, and you can monitor it too, but the laptop is not required to stay in the car. Once it is tuned, it runs by itself, the laptop is just for instrumentation and tuning, as well as diagnostic.
Please search, there is a wealth of information in the MS section here.
Good luck,
Mario