i been there actually, saw my ass down the mini rock face by the stream, lol.
cool didnt know they rent.
how about some advice on the above nutsickle, u also ride dont u?
So majority of the advise is good here.
I'd take the girlfriend with and go try the bikes out. You get a good feeling for size of bike you each need. You can go and get yourself measured and all that but i feel that's a waste of money.
You will also have to decide on the type of frame you want.
I'm currently using a GT Zaskar frame M or S can't remember, but I use it for trail riding and jumping. It's not really a jumping frame but it works well for me.
I assume you won't be jumping, or doing any hectic down hill type stuff, so those strides do look good.
Ya sure you can go balls to the wall and look for the best Shimano components etc. Will you notice it? I doubt it very much. That said I wouldn't go and buy the bottom of the range either

I'd focus on finding a bike that has disk breaks, lock out shocks that have a controlled rebound and a decent number of gears (3x9). These three things will make the most difference to you ride imo.
I would check out the hub, and see what they say.
Go look at Cajees cycles in East Rand as they have a decent variety of bikes for you to try and get a feel for what you like. Then shop around for the best price
As for accessories.
I just bought a nice Bell Venture helmet R600 ish. Don't go for that Mr Price Sports crap please

I wouldn't buy cleats (clip in shoes) yet. They do help you with power and controlling the back of the bike easier. But it's safer and better to learn without them.
Get a decent pair of MX gloves ~R250. You will thank me later
A CamelBak is also a must. I love mine. But they can get a bit pricey. So a water bottle will do for now.
EDIT:
You will also need a nice multi allen key tool,
puncture repair kit,
2 plastic tyre levers,
chain lube,
pump.