SH300 to R22
As a new pilot, I'd suggest you endeavour to do the initial training on the type you intend to fly.
The two bladed R22 is very type specific in handling and the 45 hours or so you will be doing with an instructor will consolidate that type handling and knowledge.
If you have to learn on the 300, then my view would be you should fly around a further 20 to 30 hours on the R22 with at least 75% of those hours with an experienced TRE/TRI.
Good luck with your flying.
DennisK