Generally speaking, atm most grid can benefit from at least 1 exceed to push the cap a bit higher than 1m, and it's really not hard at all to include 1 or 2 anyways since there aren't that many options. It's not until you start thinking about building your null grid and "finalizing" it that you really need to worry about how much room you have left for exceed in the remaining 3-4 slot (assuming no exceed in your main weapon type). IF you're thinking longer term (not wanting to waste your flb and +99s), I think you'd want to consider at least 2 exceed just for future growth. 3 is ideal, ofc, but perhaps a bit too optimistic for most.