There's a "stickied" thread at the top of the Orlando Hotels and Attractions forum with lots of information about the bus service at the Disney Springs Hotels. I encourage you to read the beginning, as it explains everything. Click here:
https://www.disboards.com/threads/disney-springs-hotels-bus-information.3653605/
But, here are some quick answers to your questions.
Bus service begins 1 hour prior, not 45 minutes. There are four buses running at once. The "A" buses serve the east side of Hotel Plaza Blvd and the "B" buses serve the west side. For each side, one bus goes to theme park 1 before continuing to theme park 2. A different bus goes to theme park 3 before continuing to theme park 4.
The combination of theme parks varies. For example, there could be a bus that goes to the Transportation and Ticket Center (monorail/boat to Magic Kingdom) and then Disney's Animal Kindgom. But, it's also possible that on a given day the combination could be Disney's Animal Kingdom and then Epcot.
To continue, I'll quote myself from the linked thread above:
As long as there is not any unusual traffic, if you take the first bus of the day going to a theme park, you will always arrive before the park opens. Although, if you're going to the second park, it will be close. Regardless of which two parks are coupled together, the entire trip (Hotels --> 1st Theme Park --> 2nd Theme Park --> Hotels) takes one hour.
The only exception to that would be if Magic Kingdom was the 2nd theme park on a grouping. While that's possible, I've never heard of that happening. Every combination I've seen always had the Magic Kingdom stop (Transportation and Ticket Center) as the first in the grouping.
So, if you take the first bus going to Magic Kingdom, you'll arrive at the Transportation and Ticket Center between 30 and 35 minutes later. After going through security and taking the monorail or ferry, you should get to the main entrance just prior to the official opening time.
But, if you absolutely need to be there before the rope drops at Magic Kingdom, you will need to arrange for transportation on your own.
Following. We are considering staying at a Disney Springs hotel as well. I already have ASM booked, but for a considerable price decrease I can book a DS hotel. This would be our 1st time staying off property. Any thoughts?
Make sure you're making a proper comparison in terms of hotel quality. With the exception of the Wyndham Garden Lake Buena Vista and possible the Best Western Lake Buena Vista (which is under construction), the rest of the Disney Springs Hotels are much nicer than the motel-style Disney Value Resorts.
Personally, I use Disney's Moderate Resorts as the comparison to the two Hiltons, B Resort and Spa, Holiday Inn, and DoubleTree Suites in terms of room quality and service levels.