I think this is a wonderful idea Phrenotopian! It has crossed my mind before that this sort of replication should probably lead to multicellularity rather than hunting down other cells to adhere to, and I’m glad that you have proposed this. The only issue that gives me pause is figuring out how best to implement player control over how to shape their organism after dividing or budding before entering the multicelluar stage, but perhaps that will not be needed.
When it comes to having the choice between budding or evolution I would personally prefer it to be connected with the editor rather than an option between evolution or mere reproduction. we could perhaps integrate the budding option within the editor with a potential MP cost or the likes.
I think the adhesion proteins could feasibly tie in very well with previously discussed features such as something like the Slots Concept proposed by TJwhale, or potentially the Behavior Editor.