It depends...
The approach to acquiring the tools is as individualized as need be for each builder's situation.
I started out with essentially no aircraft construction tools, so going the specialized kit route definitely made sense for me. There are several top notch vendors who offer kits, some of which are assembled specifically for the RV-12. With them you get almost all the tools you need for the -12, and equally important, none of the tools you don't need for the -12. The discount over the individual piece prices sweetens the deal, and you only have to pay one shipping charge.
Avery, Brown and Cleaveland are advertisers on VAF and go out of their way to support the RV builder community. Others are Isham, Aircraft Tool and Supply, and Aircraft Spruce. It may be worth your time to get cozy with the search function and explore some of the archives?lots of good recommendations in there.
If you buy one of the kits, you?ll find that as your project progresses there will be a few more tools to add here and there, which are not needed until later in the build. No reason to buy an expensive tube flaring tool if you won?t need it for a year.
There is one tool, though, that I recommend highly for the -12 right off the bat. Last I checked it was not included in any kit. It?s the Close Quarter Rivet Puller tool from Avery Tools, their part number 5012.
It takes the place of the little wedges that Van?s has you fabricate as the very first task in the RV-12 build. I have found it to be indispensible. Don?t go in the garage without it.
Another ?must have? is Cleaveland?s Main Squeeze manual riveter. Worth every penny and then some.
Good luck on pulling your factory together. Stay on VAF and post your progress.