I am close to having maxed out my number of DOffs. I bought the extra slots up to 400, and have around 380 now. I wonder if they will be expanding the number of slots we can buy since they are adding a new type of DOff (miners), which means there will probably be assignments for miners that we can pick up at our mine.
Should I clear out a few lesser used DOffs now to make room?
There's been no mention of further expansion with the mine, so it looks like the next opportunity for further expansion is that doff extension Stahl mentioned in one of his interviews last week. Even then, there's more reason to expect more of everything else in the system except storage.
There's not a whole lot of missions worth matching that closely, and demand for warp cores looks like it's going to nosedive as fleet's advance their mines, so there's one less. You can afford to drop a few - my top 150 or so is nothing but a revolving door for doffs heading out to the starbase.