I personally would advise against motards, they're very uncomfortable hence really bad for long distance riding, they are designed to be ridden standing up when off roading. On top of that, they're not gonna prepare you well for the big bikes. Height is not really the problem when riding big bikes, its the weight, and motards are super light.

If you want to try motards, i suggest visiting Most Fun Gym just behind Empire Damansara https://www.facebook.com/mostfungym/
Might be a little pricey, but the instructor there will teach you alot of things driving schools don't teach, like trail braking for example.

If you want to buy a second hand bike for practise, I highly suggest getting a second hand FZ150i and selling it off again when you want to move on to something bigger.

Speaking from my own experience, i took up the bike course late last year, and I had zero experience, couldn't even ride a bicycle. First day I trained on the kapchai, second day after an hour, my instructor told me to go on the 650cc 210kg ER-6n, dropped it after riding 10 meters becoz i pulled the brake too hard. And from there on I just kept training on the ER-6n, in total dropped about 6 times. Didn't get a bike to train on my own, got my license within 2 months of training, then bought myself the new Duke 390 that has an 83cm seat height, I'm 168 cm btw, and have been riding for 8 months now with it.

One advise i would have for you when training with the big bike, don't brake on the titi, don't jam the front brake when turning, try using the rear brake for slowing down and only use the front brakes when upright and coming to a full stop.