Q1: This is not my understanding. Training can only be given by an instructor. However, since there is no minimum (I think the 5 hours was a minimum under CAA, but not under JAR), if your friend happened to show you the ropes, the chances are you would require less formal training. Assuming that he doesn't teach you any bad habits that you need to un-learn, of course.
Q2: If you are flying with your PPL friend, can can not log the time because you will not have had the differences training that you need to be able to log time in this aircraft. He is P1, you are a passenger.
With an instructor, it depends on your interpretation of the rules. The rules don't say you can't log P1US, but they don't say you can, either. To stay safe, I'd log P1UT.
Q3: I guess every instructor does it differently, but this is how my checkout on a PA28R went:
For retractible undercarriage, you should cover lowering the gear as part of your downwind checks, checking the gear is down on base leg, and checking the gear is down on final. You will cover when to retract the gear on take-off, as well as the need to retract it immediately (as an automatic reaction) on go-around. You should also be shown how to manually extend the gear if the automatic mechanism fails. And maybe some other type-specific stuff (e.g. how to differentiate between a blown bulb and an unsafe condition on some types...) You will be taught the meaning of, and the values of, speeds such as Vlo and Vle.
The variable-pitch prop training should cover the reasons for using a v.p prop, and a basic idea of how it works. The run-up checks will include cycling the prop. You must learn the order in which to move the various levers and the dangers of getting this wrong, and it must become instinctive to move them in the correct order. You will probably be shown some "by-the-numbers" ways of flying the various stages of flight (take-off, climb, cruise-climb, descent, landing) as well as some more downwind and base-leg checks (the base leg checks may be left until final at a noise-sensitive airfield), but you should also familiarise yourself with the relevant parts of the POH so that you are not restricted to flying by the numbers which your instructor shows you.
There will (or should) be an element of ground-school as well as the actual flying for all of these.
This is all in addition to all the normal stuff you will cover for a type check-out, e.g. circuits, stalls, steep turns, PFLs, etc. The biggest problem I had converting to the Arrow was not the complex systems, but the extra few knots in the circuit.
Q4: The bi-annual 1-hour flight with an instructor can be any hour-long flight at all, so yes this can count. There are recommended guidelines as to what should be included, but no rules. But since the guidelines include things like stalls, steep turns and PFLs, which you should cover for any new type-checkout, your training should be a perfect opportunity.
Good luck!
FFF
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