Just to be clear, breakfast at the Plaza and CP provides no rope drop advantage.
For a 9am opening, all guests are let in by 8am and can walk Main Street up to the Hub prior to the official 9am opening. Folks will shop, get pics, stop by Starbucks, etc - and many will start lining up at the Hub spoke specific to their destination (7DMT being the most popular). The welcome show is on the castle stage at 8:55am, after which the park opens.
If you have a PPO ADR at Plaza or CP, you will not be ahead of any of this - you will be joining everyone else in the Hub.
If you have a PPO ADR at BoG or CRT, you will be ahead of the rope drop crowd and (assuming you eat and get out in time) do have a bit of an advantage in getting to some rides (mainly Fantasyland) first.
OP - I think your plan sounds perfectly legit to me, unless you are trying to be the absolute first person at the Hub spoke waiting to head to 7DMT. That crowd will have built already by when you leave Plaza. But, if you have other destinations in mind, you’re good. The Hub is generally not a crushing mad house at this time and the other spokes are manageable. I personally find this 8am-9am time on Main Street/the Hub to be one of the more pleasant experiences you’ll have all day. Generally speaking.