Hey mate, I am sorry but I don't know what to suggest about your riding, but as for your dad's view on second hand bikes, then maybe you can explain to him that using a reputable place to purchase the bike, for example off the for sale thread on this forum when you become validated then you are likely to get a good quality working bike, with a better build-up of parts than one straight out of the shop for similar pricing.
The Onza Rip you mentioned with no hydraulic brake mounts, can have an adapter fitted. Click Here. This bolts to your v-brake mounts and allows the hydraulic rim brakes to be fitted instead.
Hope you get a bike soon!!