DFT really isn't worth it unless you're fighting 4 tanks and an ADC. Even then it can be worth it to run SRS instead so you can run past them and murder the ADC, or kite back easily.
Don't ALWAYS ignore SV. SV is a great buy if you need the sustain to function in the match-up. An example would be pretty much any AP mid. However, if they don't have extremely long range AoE poke or aren't pressuring you, you're better off with Abyssal because it spikes your damage very, very hard, and only gets better as the game goes on with his other itemization.
If you're against all AD, SV can also be good if someone else on your team already plans on buying Abyssal. However, it is not a go-to rush anymore.
SV is back to a situational item on Vlad. You can't build it early because you end up with no damage then, and that's all Vlad has to offer. You can't build it mid-game because you need Zhonya's+Rylai's, then likely Void staff. Late game it won't be enough to change anything, so you're probably better off grabbing Deathcap and Void if you didn't grab it earlier.
It can be a good buy, but it has to REALLY be worth giving up the damage that Abyssal offers. Especially since Abyssal+Void is going to stack SO much better next season.
Same with Protobelt. It is not going to be a damage item next season. It'll be extremely situational.

is going to be your normal end-game build, unless the enemy comp calls for something different for whatever reason. Build them in whatever function is highest in demand.
If you get fed early, going for an early large rod lets you 2v1 if a jungler decides to pressure; also denies any damage shut-down due to cowl+D-shield. The early Rylai's from that helps even more.
Otherwise, Ionian+Codex is your go-to first buy.
Start boots+4 pots in the large majority of match-ups.