Hi RC
Hope the Wx is going to play ball!
If you are current and well adjusted to the rest of the PA28 range you will most likely have very few problems.
I found the transition easy and that is exactly what Mr Piper's aim was.
Just take on board the numbers and fly them and you'll be well on your way.
Take time before you even start the engine and sit in the cockpit for say 30-60 mins and get yourself climatised and find the different knobs and switches. That will save you time and money!
If your new mount has significantly different equipment than anything you have flown to date, make sure that the instructor explains what the functions are (again most of that can be done on the ground)
Although your instructor may teach you to fly the machine on square settings for simplicity (and in my opinion there is nothing wrong with that to start off with) the proper cruise settings can usually be found on the reverse of the sunvisor (and always in the POH)
Once you start using the Arrer for what it is intended, longer trips, it pays to have a look.
Your instructor will no doubt explain that the three greens are dimmed when you have the nav lights switched on. Ignorance of this little snippet leads to unnecessary sweating on the part of the PIC!
Main thing is to have fun, and ensure that your gear is down
FD
PS: If it is an arrer 4 you will notice that the machine will need quite a bit more runway than a 3 or any other PA28. It is for good reasons that they abandoned that concept again.