If going off road then you will need a certain amount of quality on the bike. The two main things are the suspension forks and the wheels. Not saying you are going to get these with a "Known" brand either as these parts cost. I am not talking Top grade but the forks should be rebuildable for servicing and not sealed units and the wheels will have to be strong. Not the sort of thing that normally comes on a low grade bike.

I am not as short as you but on MTB's have pretty small bikes. Easy enough to adapt a bike that is nearly small enough by fitting riser bars and short bar stems and Inline seat posts that bring the saddle just a bit more forward but riding one that is too large is not the wisest thing to do- so make certain you do get the right size bike.

On brakes- I still use V Brakes and not discs and never found the necessity for disc brakes other than Rim wear on the wheels. Except on the Tandem but that is a different king of beastie.

Take time on your bike selection and even more so- take time in finding the right Local bike Shop (LBS) It is the LBS that is the problem. The right one will be able to advise you correctly on the bike and then help with any fitting issues that may arise.