From what I've read and my personal beliefs, no, you can't overfeed a bf baby (unless you're supplementing with bottle - EBM or formula).
If his A time is still too short for a 3.5 EASY, then I wouldn't push it, however, you can always vary the EASY throughout the day if you really think he's not hungry (EAS, then AEAS, etc.). But if he takes a good feed and he's sleeping well and happy and gaining weight well, then I wouldn't change a thing that you're doing!
As for the time he sucks - I suspect it switches from eating to comfort. Watch his jaw for long slow sucks with pauses - that's when he's swallowing. When he starts doing short little fast sucks, that's probably just comfort. You could do breast compression to see if he's still interested (there's a link in the FAQ about it), or take him off and see how he does. He might be done eating and ready to play!
Sounds like you're doing great listening to his cues!
