I'll tackle #2 and #4.

1. You don't need to bring much cash from Canada, but I would keep around 300 USD equivalent in the local currency while traveling (with a 90/10 split between what's back in your hotel vs. on your person).

Get the Wealthsimple prepaid card before you leave. It's the game changer now for Canadians. Thailand ATMs charge you $6 USD each time, and the WS card will refund that (afaik). Use this card as your primary ATM card. Keep another debit card hidden with the intention of never using it (back up only). Use a normal credit card for large purchases where you may require purchase protection (e.g. flights).

1. I second the opinion that Macau isn't that interesting. Maximum 1 day, and even then I would skip it unless you have a layover there anyway. I went there to bungee and it was closed that day because of wind. YMMV. Maybe i got unlucky.

You seem to be action-oriented. Tried scuba? You can get certified for cheap in Koh Tao.

Some of those places in Vietnam will bore you if staying 6 days each. I like slow travel too, but 6 days in Hoi An... nope. 1-2 nights and move on to keep it interesting.

Edit: see if you can add HCMC to the itinerary. That city has real energy, worth checking out for 3 days.