Lets break these issues down a bit more
Left the seatbelts untidy -something i never usually do!
Not the end of the world if this was the only thing, but it wasn't, and it's not nice to leave everything a mess. If the next guy only wants to fly solo he has to tidy and secure all the other harnesses, which is a pain for him.
Left four switches on (but not the master) -American switches, i turned them off, but can remember looking back that i turned them back on again as i exited the cockpit after looking them and thinking they was actually in the 'On' position!
Which four? If it was avionics, then I can see them getting annoyed at you, as leaving these on during engine shutdown doesn't do the radios any good (perhaps people doing this over and over has contributed to the radio problems?). Also, if the next guy jumps in and flicks the master on, whatever those four switches are will also come on. Say it's Pitot heat, again not good to drain the battery in this way. I feel they have a pretty valid point on this one, as not leaving things switched off and safe shows that you haven't followed any checklist or procedure here, which could be an indication of other aspects of your flying.
Left the throttle friction tight -however i had not used this at all!
On a PA28 you really don't use this, so I don't see their point here, nonsense and nit picking I guess.
Flew an hour on just the Left tank, however i did forget to change tanks after 30min but i did select Right tank before arriving in the ATZ of base, i re-selected Left tank after shutdown.
This could be a big deal, as it is rather against the POH advice. I can see how it happened if all you've ever flown is a cessna, but you need to work checking the fuel into your work cycle, particularly if planning to buy an arrow.
Left the driver door unlocked (never had to lock a door in 60hours of training -habbit!)
Probably the fault of whoever checked you out/introduced you to the group, all flying clubs leave aircraft unlocked, many groups do too, so why would you expect any different. Just like most clubs leave the fuel cock on when owners may want this off.
And i left the excess straps on the A/C cover loose and not tucked in -This i was not told about in my check ride as the instructor told me to go to the ATM for his payment whilst he re-fitted the cover!!
This is only really a big deal if it was windy, as the excess will flap around and bash the side of the aircraft. What was the wind that day? Did you park it into wind?
All in all, I'd say a ban was pretty harsh, and they should've just raised these points on how the aircraft should be left and give you another go. If this was truly a one off as you've outlined then it certainly seems unfair, perhaps best to move on.
Why on earth would you want to buy an Arrow? It's just a heavier more expensive warrior, and you can get some very nice IFR kit in a warrior which is far cheaper per hour, and per mile flown.