First AG brew, couple of questions

I'm doing a one gallon AG kit from AHS (Stubby Oatmeal Stout). Estimated OG was 1.058, actual was 1.045. Estimated FG was 1.011, current (3 days after brewing) is 1.014. I think my OG was so far off because I misjudged my boil off rate and boiled down from two gallons to just under 3 quarts; I added the necessary water to bring it up to a full gallon just before pitching yeast. It was BIAB, and I very well could have done something wrong, even though I did what I've read on here. Anyway, that's just the usual information everyone asks, so I decided to put it up front.

My real questions are: The hop aroma and flavor will mellow over the next few weeks in primary, right? I'm planning on not messing with it until Saturday after next, or perhaps the weekend after that. I'll bottle and condition for two weeks before chlling and drinking one. Hop front taste is "green" (obviously, after only three days in primary), but once that's past it's a really great oatmeal stout taste. This is going to be a great beer when it's done.

The other question, the big question is: SWMBO asked if I could put vanilla in it and make it a vanilla oatmeal stout. And I said, "Challenge accepted!" So, how do I do it? I have (Honduran) vanilla extract, but I think I know where to get some whole vanilla beans. Which do I want? How much? Do I add to primary, or do I wait until bottling day?

Thanks for the help!

You may have not mixed well after adding the top off water for the lower OG.

It will mellow out more when bottling condition, and I'd recommend 3 weeks on that not 2.

Typically the vanilla is added in "secondary". I'd search for some recipes on here that indicate amount, but I'd wait for 10 days after brewing to add the vanilla. You can leave it in the primary container and just add the vanilla. Leave it there for a week or so and bottle after.

Okay, thanks.

I added the extra water before aeration, which is the "shake the bucket until your eyeballs pop out" method, so it is mixed in. But I'm not terribly worried about it at the moment because I think it will work out okay. When I get ready to do my next batch I'll see what I can do to avoid it.

Would you add extract, or beans?

I do a Vanilla coffee stout for friends. I generally have it sit 2 weeks minimum in the primary for fermentation to complete and the yeast to clean itself up. I then transfer it to the secondary. I slice the bean length wise and scrape out the guts. I cut the bean into smaller sections. I then toss the whole thing in the secondary inside a hop bag I sanitized with Starsan. Vanilla is crazy powerful. There is a big difference between 7 days and 10 days so keep an eye on it. You don't want the vanilla to overpower the whole beer.
Just my 2 cents.