Hi Parkway - welcome! Lots of threads on here already on this subject. I don't think its really RPL vs PPL, as one is just a continuation of the other. The 6 hours you have done will absolutely count towards the RPL. If you get the RPL, i believe that already includes the radio and ability to carry PAX, just in a limited radius. Once you start taking Nav lessons, yes the cost will start creeping up - but not sure there is a separate nav endo for the RPL - you need the PPL if you are going to go farther. so if you are happy with 1500kg and a limited radius, then just stick with the RPL. Once you want to stretch your legs a bit, then you can start working towards the PPL.
Aeronautical experience is aeronautical experience - as long as its logged and with an instructor, and right class of plane, it will count towards your total required hours.