The play in the front rotor is normal. Compare it to other bikes when you get the chance, if it's about the same, no worries.
If the leak in the exhaust bothers you, get it welded, otherwise ignore it.
A little up and down play in the swing arm bearings is normal on a GasGas but you should check if all the bearings (swing arm and it's dog bones, wheels and headstock) are greased properly and not corroded.
Replacing the bottom out rubber isn't that easy, you need to remove the spring and the upper mounting eye of the rod.
Regarding the bars: how tall are you?