I am so, so sorry for your loss but I'm happy for you that you are looking forward to your future for happiness. I went to WDW a few months after suffering tragedy a few years ago and it really did help. ]ust be sure to cut yourself a little slack, ok. When we were at WDH on that trip, at first, I kept trying to smile for the kids sake but would still tear up because I was a bit sad I just wasn't myself. But, eventually, I began to smile all on my own and when the real smiles started coming I knew I'd be ok, and now I am mostly

Kids have amazing healing powers
Another trip, I went alone with my kids when they were 3 & 4 (DH couldn't join for 4 days in 2002) and I was terrified. Never did anything alone before. But, you know what, it was a great experience because I had them all to myself, no sharing, and I LOVED it. Back then I had to get a car service because I just didn't know how I could watch them AND my stuff. The car service got my stuff and I watched my kids. Now, there is the Magical Beginnings Service which would totally smooth out my biggest hurdle. All you need to do is get your stuff to the airport and you're home free
As for rides, I told DS that there were things he just couldn't do because DD wouldn't do them before the trip so there was no arguing when we got there. I also have a long standing agreement with DD to try 4 new rides per trip that she ordinarily wouldn't do so, at this point, only the coasters are left as no go If your kids will go on all the rides together the 2nd biggest hurdle is also resolved.
Overall I totally think that going to WDW will be a great event for all of you.
Anyway, I'll keep checking this post back in case you need support.
Here are some DIS

for you and your kids.