All you need to know.
For the "With Thailand now in mourning" point, do explain it's due to His Majesty's passing. Tourists might not know this.
Grand Palace really is closed these days (or at least difficult to visit for a foreigner).
Ping pong shows (at least in Patpong 2nd floor bars) are always a scam, so "watch your bill" is insufficient advice. No matter what the touts promise, they will try to extort a hefty amount from you, and it will certainly get ugly. While it's possible to talk the price down, it's not an experience an average tourist would appreciate.
With jet ski rentals, simply "pointing out dings and scratches" won't get you out of the scam, if they're intent on scamming you.
There's no need to pay 4000 baht for a khlong tour. You can get one on the weekends from Taling Chan market for 100 baht per person.
No need to recommend against all floating markets. Sure, Damnoen Saduak is a tourist trap, but Amphawa, Bang Nam Pheung, Kwan Riam, Lad Mayom and Taling Chan are colorful, fun, and fairly cheap too.
Regarding food, you absolutely have to mention Talat Rot Fai 2 next to Esplanade MRT. Never seen a bigger variety of food in one place in my life.
A warning about taking tuktuk suggestions on a restaurant (especially the Somboondee scam) is in order.
As a general warning, it's good to avoid non-packaged food at bus/train stations.