If I Recall Correctly, Big Thunder Mountain Railroad
basically offers FP when it's busy (weekends/summer/etc.). I'm sure there's more to it than that, but it may or may not have FP at any given time.
Assuming there is still no Fastpass enforcement, I'd definitely do DLR29's order, but Space Mountain is always a priority for me. Getting a FP for your top priority first is not a bad idea at all. As long as your top priority isn't Roger Rabbit's CarToon Spin.
If Fastpass enforcement were in play I'm not sure what order I'd do, but I might still do DLR29's. You'd get a FP for Space Mountain, have about 50 minutes to do whatever (Fantasyland? Nemo subs?) and then head back to get a Star Tours FP and then ride Space Mountain. If it's warm out, you'd get Splash Mountain's FP earlier because they'll go quicker and it won't be cold when your return time rolls around. If it's chilly out, you'd get Splash Mountain's FP later because hopefully when your window opens up, it will be warmer.
Now, if the return times were being enforced, I'd probably do HMH's FP with a return time in the evening, if possible, because I think it's just a little more fun to ride HMH at night. So maybe slip Big Thunder Mountain in there as a "filler" if needed.
Have a great trip!