The Robin or Slingsby are good aircraft to start on and will keep the cost down, as they are harder to fly basic aeros you tend to develop good technique (though IMHO the C150 takes this principle TOO far). If you go for CAP10/Pitts you will probably combine the conversion with starting the aeros - at least that is how I would do it (ie. 1 hr lesson with 15-20 mins off aeros and the rest on the other conversion work). You will probably find that 20-30 mins is more than enough aeros for one session, especially at the beginning