We are all adults and don't care anything about the shows. Never rode TSMM but Ive heard its like Buzz Lightyear which we can ride in MK. Would we be able to do those 4 things and leave by say...2pm? Maybe sooner? We can get there at opening and will be traveling the 3rd week of October.
Also, I've never park hopped before. How long does it take? I guess we'd exit DHS and get in our car and drive to MK's parking lot? Staying off site.
You can absolutely get all of HS done in a half day. We have done it many times.
Picture TSMM as a nice juicy steak. Buzz Lightyear is a Mickey D's cheeseburger that's been sitting under a heat lamp.
You don't mention your plans for FP+. If you used your 3 FP+ reservations at HS in the morning, you could easily get in multiple rides on everything before noon. Then you can make a FP reservation at a kiosk when you get to MK. If you did this option, note that TSMM and RnRC are on the same tier, and you can't get FP+ for both. Also note that you cannot get a MK FP until you get to a kiosk in MK, which means the earlier you get to MK, the better. If I did this option, I'd be inclined to have lunch at MK instead of HS.
The other option would be to ride everything in standby lines at HS, and have your 3 FP+ reservations waiting for you at MK. Note that TSMM and RnRC are the longest lines, lots of people are going to be headed to those two. Star Tours is going to have the shortest line. Note also that RnRC has a single rider line, which is great if you don't mind not sitting next to each other. Without FP, my plan would be TSMM first at rope drop. Then compare wait times RnRC/ToT, either ride RnRC then ToT, or ToT then RnRC single rider, then Star Tours. You wouldn't get a second ride at TSMM or RnRC without a long wait (or single rider RnRC). You could be out of HS by 11am if you wanted to.
Personally, if I was trying to plan my HS/MK days, the last thing I would be worried about would be a Sci-Fi lunch ADR. I would pick the day that's best for you, what you want to do with FP, and figure out when you want to hop. If there's an ADR for Sci-Fi at the right time, great. If not, there are plenty of counter service places in HS and MK where you could get something to eat quicker and cheaper.
Regarding hopping from HS to MK, the MK parking is at the Ticket and Transportation Center, depending on where you end up parking, you might need to take a parking shuttle, and then you will need to take either the monorail or ferry over to MK, so it's not super quick. Note that once you pay ($17?) to park at HS, you will not need to pay again at MK.