autos can be tricky, they are easy to stunt due to having very little veg time to recover, a lot of auto strains only require half strength nutes and will suffer if given more, its best to start low and add as and if needed
do not top an auto, bend/lst if you are worried about hight
Get a KC 45 auto. Biggest I have ever raised. Will get 7ft. Some act more like full season plants than autos. It will yield so much more than a regular auto.