Barnstormer-actually this is 36”height limit)
Barnstormer's height requirement is 35". Not a big difference, but makes it more likely a 2 year old can ride.
or can order a separate FREE kids meal at TS.
Generally, no. A couple of non-buffet character meal restaurants frequently allow an under 3yo to order a free kids meal (CRT, Akershus, and Bon Voyage breakfast have been known to do so), but it's not an official policy and doesn't always happen. Other non-buffet TS restaurants do not generally give a free kids meal to under 3's. Disney's official policy is kids under 3 are free at buffets and AYCTE restaurants and can share a parent's meal at no charge at other restaurants. If you wish to order him a separate kids meal, expect to be charged. Most TS restaurants will provide a free kids drink to little ones, but even that is considered pixie dust and is not guaranteed.
OP, my best advice is to take cues from your grandson and enjoy the day. The parks are so magical when you experience them through a little one's eyes. We took my son a few days before he turned 2 and it was amazing seeing him come out of his shell and notice things we never would have taken the time for. He loved watching the ducks, pointing out the light fixtures everywhere, and finding Hidden Mickeys in the architecture. Definitely take things slow and don't be afraid to throw the plans out the window.
Second, every kid is different. Mine fell asleep on iasm and the Carousel as they just couldn't hold his attention. He LOVED POTC and laughed the whole way through HM. He loved the fur characters and ran to every one, including those he had no idea who they were. Face characters freaked him out though. Rope drop never would have worked for him, so we got to the parks around 1030 and stayed till close. The point is, every toddler is different and you may not know what he will like or dislike ahead of time and he may surprise you while you're there. The great thing about that age is unless they're overly tired or hungry, most times grumpiness can be remedied with distraction. Point out something new for him to look at or let him stretch his legs for a few mins.
As for changes in the last decade, I'm guessing FP was paper last time you went. It's all digital now. You can select 3 FP in advance for each person per day, 30 days in advance if you're staying off site and 60 days for on site. Under 3's do not need and cannot get FP; as long as the accompanying adult has a FP (and it's a ride the kid is tall enough for), then they can enter the FP line with the adult to ride. After you've used your first three pre-scheduled FPs, you can go on the
MDE app from your phone (free WiFi in the parks) and schedule more FPs, one at a time for the rest of the day. The app also shows current wait times for the rides and shows, which could be helpful if you're in Fantasyland for example and considering an attraction on the other side of the park.
If you have magic bands (provided free to on-site guests or available for purchase), those will be used to scan in for FP. If you don't have magic bands, your park ticket will work the same way, so make sure you keep it in a safe but accessible place.
If you will have another adult with you and you wish to ride anything that the toddler is too short for, rider swap is available. The passes are no longer paper but digitally added to your magic band or ticket and will then show up on your MDE app. You can only have one rider swap at a time.
If you want to eat at any TS restaurants, reservations open 180 days in advance. Many popular places book up fast, so reserve as early as you can if there's a restaurant you really want. Several of the quick service locations offer mobile ordering through the MDE app and this can help you to beat the lines (really nice with a little one). Also, all of the quick service locations offer free cups of ice water which is great in the heat. Disney as a whole has also for the most part stopped giving out lids with drinks and only offering paper straws which can disintegrate quickly, especially with a toddler chewing on them. You may want to consider bringing a sippy cup or water bottle with a lid for your grandson and just transferring drinks into there.