I hate to say this, but the scenario you present is a very difficult scenario to plan with G+. You want to ride the top 3 attractions in each park, the attractions whose G+ selections are the most unpredictable and sell out the fastest. Planning G+ is difficult for one park hop, and is almost impossible for a second park hop. You really have to go in prioritizing which ride you want to stand in line for and which you want to G+. Problem is, we can’t answer that for you. You would have this same problem with Fastpass+, so it’s not entirely a G+ issue.
With that said, I will explain the morning rule first because it plays an important factor. At 7am, you can make your first selection. However the screen that lists all the rides will not show return times between 7-7:30. Only when you get to the confirmation screen, will you see the actual return time. In the past, at 7am the refresh screen would show Slinky with a return time of 8:30, when you selected it, it would show 10:15, and the confirmation screen would show 1:45. This made thousands of people upset, so Disney hides those first two times and only provides the return time at the confirmation screen.
So if you are trying for a 2:00ish return time for Remy or a 6:00ish return time for Slinky, this makes it incredibly difficult to predict when those return times will appear in the first 30 minutes. We all know they book fast, but none can see how fast unless you book, get the confirmation screen, cancel, and repeat. If you want those return times for either of those two rides, this is what you will have to do between 7 and possibly 7:15ish.
What will also happen is that at 2 hours after park opening (either 10 for HS or 10:30 for Epcot, you make your next selection. As we all know, Remy and Slinky will be fully booked, therefore it is unlikely you will get the other unless you refresh. Again, you would have had this same problem with Fastpass+ had you prebooked Remy or Slinky, so this is not a G+ issue.
I see a couple of scenarios. If you don’t care about Slinky, then try for an after 2pm Remy (if all you care about is world showcase, take a bus from MK to Beach Club and enter through IG rather than taking monorail to the front of Epcot). At 10:30, try to get a quick return for a MK ride or two. In the mid afternoon, try for MMRR. TSMM will be easy to get in the late afternoon.
If you have to ride Slinky, get it first but it will take you about 5-10 minutes of booking and cancelling to get an after 5pm or so return time. Standby Remy, and do the same as I suggested above with MK and HS.
Adding Jungle Cruse to the mix makes it even more difficult. In theory, if you book JC first and get an early return time like 10am, you could do the same scenario as above, book another MK ride afterwards, standy Remy, and try for MMRR and TSMM later in the afternoon.
I consider myself an expert at Disney planning, but even this scenario you provide makes my head hurt.