I don't notice a loss of damage, just due to how hard it is to proc thunderlords. Realistically, you have to AA twice, and Q to proc it for 40- damage early, with a lengthy CD. I found it was cumbersome before the rework, and worse off now. I dislike DFT since it draws tower aggro, and you'll typically end up tanking tower shots by accident.
Visage is a really good item, but I'm not going to say it's necessary. It's incredibly good, not something you want to skip, but you can. -- Typically take the 5% CDR, but the Mpen isn't bad either. CDR scales better thou, imo. -- I tested a protobelt rush build on Vlad a week or so ago, and it worked pretty well. Gives some nice dueling potential, outplay potential. With that said, I'm not running it in my build rn. I've been testing better with a rlyai's rush.
Runes I've been testing a lot also, I've mainly been running a standard mage page. Also testing a tank-scaling page, with %max HP. That said, I have no idea what's the best page. A lot of people are going to argue CDR heavy pages, but the loss of tank stats wasn't testing well.
Items are subjective. You build what you need. Rylai's gives damage/sticking potential, Zhonyas gives survivability. Abyssal, Liandries, Protobelt, Deadmans, Visage. -- Starting items, I've been going Dark Seal + Refillable. Seal gives snowball potential, AP, and resells pretty well. Refillable is cheap and efficient.
The build I've been running rushes a haunting guise, so I've been taking Sorc boots to have better damage mid game. Swifities are probably better though, or Lucidity if you need the CDR to cap out.