SPG members/card holders, lend me your expertise

We've never stayed at the S&D before, but after a recent trip at BWV (renting dvc points) saw that S&D would be just as convenient.
So...when the S&D was running their superbowl promo we booked a stay for june (3 nt anniversary trip) and october (4 nt beginning of a split stay family vacation).
Also, we just decided to do a few days at flower and garden so we're headed down next month.
Question #1
Applied and got the Spg amex card. It has a thing where you'll get 35,000 bonus points after the first 3 months if you spend so much. If I'm understanding correctly that should be about enough for 3 nights? I'm seeing its 10k to 12k per nt?
Yes, as soon as they credit your account for those points you could use them. For Swan, it's 12000points / night and for Dolphin it's 10000 points/night currently.
Question 2
Can i apply the points to one of the reservations i already have? Or do i have to re-book? This is more doable on our june trip, but in October my dates are locked in since it's the 1st part of a split stay and we booked dolphin bc we'll have 5 in the room.
You will have to rebook. When you use points, they only have certain amount of room available vs. cash so rebook.
Question 3
How do I effectively rack up more points?

I think I saw on here somewhere about charging to room etc...
Best way to rack up points is have SPG Amex card for credit card at the check-in and start charging to the room while eating/speding something at their property. Also, referring the card to friend helps if they open one.
Last one...
I've also seen here about asking for a room upgrade nicely, what's that about?
Usually at the check-in your reservation will be linked to your SPG account and when you give your SPG Amex card for charging incidentals, they will mention something. At the time you could say something like "Hey, by the way, do you have any upgrades available?" It's worth a shot. Worst is no.
Thank you all so much I've enjoyed browsing this thread and finding out more about the S&D, I think it will be a great fit!