The helmet will just depend on how much you value saved time. I think it’s true to say that any aero helmet will reduce drag compared to a bog standard one, although finding the optimal one would take some testing. An aero helmet is often considered one of the more cost effective ways to buy free speed. But the question to ask is does 5+ minutes of saved time really matter to you? There’s also the question of your race. If the conditions are hot, and you are not used to it, spending 6+ hours inside an aero lid might get uncomfortable.
Personally, I like an aero helmet with a visor as visibility is better than looking through the top of sunglasses.
On the saddle, it’s going to be a matter of personal preference, but yes, there are lots of TT specific saddles. Mostly with central cut channels to relieve pressure and/or cut off noses. I tried an adamo but hated it. I now use a fizik mistica, having previously been on the tritone. But most brands do an equivalent so it can be a bit of trial and error for what works for you comfort wise.