Congratulations Kiwi Stoker!

I don't know the answer to your question because I'm just trying to figure it out myself. DS is 9 months old and weighs 15 pounds. Right now he is starting to get really mobile -- quite a bit of pre-crawling, so one consideration is that I do want to make sure he gets a significant amount of his own "playtime" so that he can move around and develop his motor skills. Spending hours confined in a baby carrier or a stroller or carseat or bike trailer might not be conducive to that.

Right now he will nap for 40+ minutes in the afternoon, in a stroller or strapped to me in a carrier, when I take the dog for his walk. If I didn't have to walk the dog I would probably be exploring some kind of bike trailer option right now. Also, he still needs to eat quite frequently. The logistics go something like this: feed (20-40 minutes), change diaper, feed myself and use restroom, change diaper again, get dressed for going outside if I'm not already, clean up mess that baby made while I was taking care of myself (latest trick is to overturn a pitcher of water that we keep on the coffee table - which means yet another new diaper and a new outfit), make sure diaper bag is stocked, bundle up baby and strap him to me, or carry stroller down steps and strap baby in. So by the time we are ready to start our walk we may have at most 1.5 hours before he needs to eat again. So when we are out I either need to find some place warm and dog-friendly where I can nurse the baby or I have to get home. Yesterday we had him out with us in central London for about 5 hours. He did okay, but didn't nap like he usually does, so that had repercussions for our evening routine.

So basically at this stage I could see doing short, < 2-hour rides with the baby. Of course this means I would need to go bike shopping, since I left all my bikes in the US.

One question I have about bike trailers is whether or not they allow a baby to sit rear-facing. For car seats it is recommended (required in some places) that kids sit rear-facing until at least 2 years of age, because of the neck stability issues that others have mentioned. Given that you could get up to a decent clip even trailing a fair amount of weight, I'm wondering if rear-facing might also be a good idea for bike trailers. I'm pretty sure I've only seen forward-facing on the street, but I haven't done a whole lot of research.