New to cycling and looking to get a bike

[RAEN]

Hi all. 

I have a very old Avalanche ATX 250 that I got when I was younger as a gift. Fast forward a lot of years and I've started riding around work (I work at a school and I find it safer to ride around the school grounds than to ride on the road) and I'm starting to enjoy it. The thing is, my bike is obviously not great. It doesn't even have front suspension. I think it might be a youth bike because when I tried to figure out the frame size it has size 16 on it. I'm looking to get a new bike that has some front suspension. I don't want to spend more than like R6000 on a new bike because I don't know if the cycling thing is actually going to stick. I'm probably not going to be doing much trail stuff, but I would like a bike that wouldn't fall apart if I did try out some casual trail riding. Because my bike would need to fit in my car for transport reasons, I'd need quick release wheels (and I'd like a quick release seat post because I'm not great at setting my seat height and I play around with it a lot). I would like to use the bike to enter some road races in the future, so I'll be changing my tyres to slicks for those and I think quick release wheels would make that job easier as well. I'm only 156cm tall, so I think I need a size small frame. 

 

I'd really appreciate some advice on bikes and brands that might work for me because I'm clearly in the dark a little bit. I know some budget brands are not very safe, so if anyone could steer me away from brands to avoid, I'd appreciate it. 

 

Thanks in advance!