Wanting to get back into biking. Where and what to buy?

[GhoulishComet]

Hello all I could recommended here by carbonite hence the new profile

I haven't been biking since highschool since I tore my meniscus and Acl and my younger cousin inherited my titan as I had outgrown it and am interested to get back into it but for now to start I will probably be using it to commute to uni from residences and join the bike club on some groups trails. I am still very much a beginner so I don't know much of anything. I plan to go more mainstream trail ridings 

I am around 1.77cm and weigh 79KG. My budget is prefereably 6-8.5K but my cap for now is 10K. I am looking to buy end of Feb and I am in Pretoria centurion side. If you have some advice on other important stuff like a helmet, shoes, knee and elbow pads or etc. would be appreciated but isn't a priority.

I don't mind new or used. What i am looking at are these Titans

https://www.pjcsport.co.za/bicycles/titan-racing-rogue-alpine

https://www.pjcsport.co.za/bicycles/titan-racing-rogue-peak

on the used side what has my current attention is this silverback

Silverback Spectra 29 (L) | Hardtail Mountain Bikes | Bike Hub