You should be in the clear from here on out, until maybe 12/20.
The big issue is timing the closing date of your first statement. The AF posts at the close of the first (and 13th/first Year 2) statement. You want it to close sometime in December, preferably at least a week into December, or later. So your first year and second year AFs post in December, giving you 30 days -- into January (2020) -- to close your card and still get a full refund of the AF.
The shortest I've seen the first statement close is 13 days from approval. It's more typical for the first statement to close 20-something days from approval. That should put you in early to mid-December if you applied today.
You also want your card in hand before the end of the year to use your 2018 airline credit.
Since you're going for the Gold card, keep in mind that Amex has been having supply issues with the new metal cards, particularly the Rose Gold cards. Consequently, a lot of people have been reporting that it's taking 10 days, 2 weeks, etc. to get their cards. I've seen DPs that Amex is extending the MSR period for these folks, but that extension won't do you any good if you need to have the Gold card in hand in December to use the airline fee credit for a SW GC. With the holidays and all the mail and packages in transit, I'd give extra time for delivery too, and wouldn't wait too long into December to apply.
The 4x supermarkets category is going to be very useful.
Taxes should all be included, but I think the resort fees are separate. I haven't stayed with a resort fee yet so I'm not sure what happens in practice, but the one I have booked right now is showing only that fee as payable and the rest of the stay is 0.
