Well trust Mr Harding to bring food into the discussion, however he is correct, an empty stomach will make you feel queasy as will a very full one. About an hour after a bacon sandwich and a cup of tea is the best time to try aeros or spins if you want avoid feeling ill. Lots of fresh air also helps.
As far as spin training is concerned I would agree that a C152 Aerobat will allow you to experience a spin, but as you will lose 1000-1500 ft in a spin you will then spend 5 mins or more getting back up to height. Do it in an Extra, Pitts etc. and you will do just as many spins but in half the time so the cost will be similar.
I would also suggest asking for a spin while in a turn to be demonstrated. This is the sort of spin that will occur when turning from base to final where you use a bit too much rudder and a bit too much pull to try and get lined up and all of a sudden it lets go.
'Normal' spins are done from a straight ahead stall with rudder applied and are much less likely to be encountered during normal flying.
Not sure whether its best during the training or afterwards. I can't see that it would make a lot of difference.