Games are huge and have to keep deleting/reinstalling them is quite a pain. Remember that even if its on disk, you have to re-download the patches, that are quite big.
As for the HDD brand, my recommendation is always Western Digital. I have 4 1TB drives on my desktop, several ones on notebooks, one on the PS3 and all are great. HGST and Samsung are also good. Seagate is pure crap, don't buy it, I've had a lot of issues with them.
If you are going to upgrade, I recommend to get a big drive that will last the gen, so a 2TB one is the best choice.
Anyway, I wouldn't recommend buying a PS4 now. It's around 350 dollars. The rumoured price of the Neo can be as low as 400 while the Slim could be even as cheap as 250. After the Slim launch, they will do a fire sale of the regular model. Actually, you could pay just a but more than the OG model and get a Neo.
