I've stayed a couple times at Harbour Lake (we're Marriott owners and love the Marriott timeshares).
I'm assuming you have a rental car, as you'll want one there.
Honestly, if you want to pop over to MK, you could just valet park at the CR and walk over. It's not so much more than paying to park at the TTC, and much more convenient!
You'd want a car to grocery shop and to eat out. Harbour Lake only had sandwiches at the bar, not a restaurant. It's a great place for little kids, but we had a car. Also did Discovery Cove, which was literally 5 minutes away (and an amazing day!).