Double vents and insulation questions

Ba11zooka

Howdy - we're about to enjoy our first New England winter in our 'new' (1889) one-pipe steam-heated Queen Anne, so I've been reading up and making plans for doing some much-needed maintenance on our system...and I've got a couple of questions!

Our system has three counterflow legs hung off of two parallel flow “sub-mains”. The two parallel flow sub-mains have old Vent-Rite #45s on their returns right before the Hartford loop, one counterflow leg currently has an old Vent-Rite #75 at the very end, and a couple of the radiators on the 2nd floor have two air vents (I'm guessing that the previous homeowner and service folks were trying to emulate additional main vents, since these two are fairly small radiators and wouldn’t need that much venting on their own if the sub-mains are vented correctly?). I've attached a not-to-scale diagram of the system for your entertainment.

1) I'm planning to replace the worn out main vents with larger-CFM units as soon as possible, but I'm wondering either of those 2nd floor radiators should keep their doubled air vents to help with main venting?

2) The header and dedicated return piping on the two parallel flow legs have no insulation near the boiler - should these be insulated? I would think that insulation would help, since there could/should be steam moving through that line and keeping the steam as steam in the return might save a few BTU, but I figured I'd check - the cellar stays warm with all of the exposed piping, which is good for preventing frozen pipes, I guess…