As I'm now on my third RV-4, I'm obviously biased, but will throw in a few observations:
Suitable for low hours pilot? - Well they are not suitable for conversion training. You can install back seat stick, rudder and throttle but it is not intended for P1 flying. Take-off and landing from the back seat is 'interesting'. But they are quite easy handling for a tailwheel aircraft, so checking out thoroughly in Chippy, Citabrias, Jodel, Emeraude, Condor etc will prepare you for the front seat. The instructor in the back won't do much more than critique. In my opinion the -4 is one of the easiest, best behaved TW aircraft available.
There is not a lot of space, no seat adjustment and limited pedal adjustment so you need to make sure you're comfortable with the fit.
RV-4s do come on the market quite regularly and usually at a lower price than the later models, but they are homebuilt so you need to check the build quality preferably with someone who understands the construction.
An O-360 and CS prop will make them pretty fast but at the expense of payload and handling. An O-320 and fixed prop won't disappoint and would be my suggestion.
Handling is 'sporty' but nothing like a Pitts. Controls are light and smooth and it trims nicely for x-country and even instrument flying (if permitted). Roll rate is about 120-140°/second.
They are pretty easy to maintain using mostly readily available parts. I think of it as like a Chippy with twice the performance and half the running cost.