I am so bad at math/dates . . . you'll be there in April? Early May? What do the crowd levels look like?
My plan was similar to others - I do not park hop, so I chose what parks I'd be in on which days based on the TP crowd calendar, with the caveat that we had to be in MK for our son's 5th birthday.
The first thing I did was look for BOG on the definite MK day. I actually screwed up calculating when my 180 day was, so I looked at 7PM Central on reservation day (instead of 7AM Eastern). I was staying onsite, and looking for BOG on our 4th day (so it was ~ 183 1/2 days out). I got BOG for 6:10 pm, no problem. Crowd calendars are 4-7 for the parks we're hitting that week (DHS is 10/10 for a few days, which we're avoiding). MK is a predicted 5 for our BOG day.
So, BOG was not an "impossible" get for me, even with my miscalculation, though it closed up pretty quickly and I've been looking for an alternate date (we've firmed up our park plans and I want to do BOG on our other MK day now). I've seen that BOG can open up for others within 45 days of travel, and the week before/week of travel, so keep hope alive.
Other than BOG, I have had no problems at all tinkering with every other dining reservation at dates within less than 180 days. I got a pre-rope drop Crystal Palace for our son's birthday, well after 180. I didn't know about the Fantasmic dining package until after 180, but got Mama Melrose for lunch no problem by continuing to check, at about 150 out. I'm at about 82 days out, and still tinkering, with no problems finding character meals like Garden Grill. The only reservation that I've kept the same since my 180 day is BOG. Otherwise, I've found lots of flexibility to switch things.
My crowd levels are around 4-7, so I'm not going when it's a ghost town. However, there was no "free dining" or dining package discount promo announced when I booked most of my ADRs. I think this, more than crowd levels, can affect what's available to you.
Personally, where I don't have an ADR scheduled, I have in my personal Touring Plan a meal break with notes about what are some good counter service options (e.g., Columbia Harbor House in MK, or Sleepy Hollow chicken waffles, etc.). Don't forget about resort meal options.
ETA: The MDE app did NOT work for me with ADR booking at 180. This is why I missed the morning of my ADRs, the app (on my iPad and phone) was showing that I could not book yet. I was tinkering on my PC and saw a BOG opening and was allowed to book it, then freaked out and realized that the app was not correct. Do not plan to use the app for your initial bookings, IMO.