Does he have a cold? Is that what is causing the stuffiness or is it most likely something else? You might try elevating the head of wherever he sleeps (or get a wedge or some sort) to help with the stuffiness -- aside from that, saline, humidifier, etc is the best you can do at this age.
If you suspect intolerances, many moms find soy is a problem as well as dairy. How are his poops? There's some info on intolerances here:
Does my LO have food intolerances?Have you ruled out reflux as a possible cause of the fussiness? There's some good info on that here:
Reflux 101 - General reflux information that you can have a read of and see if anything rings a bell.
Regarding the cluster feeds, it's the kind of thing that works really well for some babies and they carry on for many weeks and doesn't work at all for other babies. So if it's not working, you might try dropping it. In the case of my dd1, she was so fussy in the evenings that frequent feeding was a good way for me to keep my sanity, so I fed often.
It's the kind of thing where you keep it until it's not working any more -- very vague I know, but it seems to differ widely.
And finally, don't buy into the idea that bigger babies need less feeds. My ds was my biggest of my 3 and he fed more often than the others at night. I tried to fight it for weeks and weeks and then just realized that he honestly seemed to need the calories.