The original question was whether someone with no aircraft experience should build an RV-12 and make mods. My answer is that you can build that particular plane with little experience because all holes are predrilled and the fastening is easy and the wiring is already done with connectors; all the thought processes are done for you. But I would not recommend doing any aircraft mods if you admittedly don't have the judgement to know what you are doing. As far as an injected 912 is concerned, the cost and weight is more than carbed engine and the carbed engine works fine so unless there is some reason currently undisclosed, the 912S is the engine of choice. Remember that the RV-12 is certificated to be built exactly as the factory specified without changes or mods. It is not like a standard experimental which requires 40 hrs of flyoff; it only requires 5 hrs flyoff because no changes allowed to original design.
If you want to get into aircraft construction, get smart and start taking builder courses thru EAA workshops and work with experienced builders to understand the basic technology. Flying in a plane you built is not like building a car where you pull over if something stops functioning.