Sure I get the not waking them thing! It was just an alternative to consider but if you want to stick with a (hopefully) long first nap then just make sure that first A time stays at a good 3h even if hubby starts the day early - if you allow a long nap after a short A time that can actually contribute to early wakings as LO uses the first nap as an extension of night sleep. As long as you stick to a good age-appropriate A time though you should be ok.
He doesn't seem to be affected by the A time before bed and will get sleepy and cranky usually by 6/630 no matter what. I remember sticking to a 12 hour day with my first lo which means 6 wake up and bed by 6 but isn't that a bit early?
I'd get him into bed when he's tired - no point in keeping him up later if he's clearly ready to sleep
I personally think 6pm is a fine BT for a baby, but some people prefer a later one - really it's up to you. And of course if he naps 2-3.30, 6.30pm sounds fine. 12h day is a good guide, but do bear in mind some babies aren't really 12h night sleepers. DD was, DS more of an 11h man on average. So a 12h day for DD was great, for DS it caused issues and making the day longer was better for him. That said, he did nap rather better than DD...swings and roundabouts hey?!
Sounds like you are handling the early starts just fine. DS did very similar at about this age, and we would ignore him if he was awake and happy, or try a feed and put back down. Sometimes I just lay on his floor to keep him quiet until an acceptable WU time, for us 6am absolute earliest, and ideally 6.30am.