Bulkhead and Ledger question

Two separate questions. I'm entering into the DIY world, have done a couple basic projects - deck, fence, entertainment unit. I'm getting ready do add a couple more projects, but am getting some advice from a friend of mine that I'd like a second opinion on.

#1 - The shed I'm building is going to have a couple doors, one with a 4' span and a second with a 6' span. My original plan was to go with a laminated 2x6 lintel supported by double jack studs on the 6' span (K J J lintel J J K) (where K=king and J = jack studs) and a single jack studs for the 4' span (K J lintel J K). He's suggesting that I should carry the lintel to the next set of studs over like this: K J J -16 oc- J J J lintle J J J -16 oc- J J K. Does this really make it that much stronger? I haven't heard of carrying the lintel to the next set of studs after the framing of the opening. Is it common? It looks like only a bit more work and wood, but I'd rather not make sawdust for nothing.

#2 - Framing in my basement ducting and support beam which all run side by side. I was planning on framing it out using 2x4 except for under the ducting and beam where I was just going to use either 1x or sheet it with 1/2" plywood before drywalling it because my beam and ducts are only 6' 4" from the floor. He suggests that this won't be strong enough because the bulkhead has a 46" span before the framing. I really want to maintain as much head clearance as possible since I'm 6' and my brother who visits us is 6' 3".

Any thoughts on the matter would be appreciated.