On a proper laptop now so I can reply properly. (I've been typing on my old one where half of the keys don't work, so I've had to copy and past in letters and punctuation!)
Thanks for the replies so far. It's going to be a nightmare enough as it is, OH shift works, and a lot of the work is at least a two man job. I'm already 26 weeks pregnant with an incompetent cervix, so I'm worse than useless in any practical sense with the vast majority of jobs. As such there are going to be some days where we're just going to HAVE to cram in as much as we can. If OH is off, and we have an offer of help, we can't waste that. That being said, we have a just turned 2 year old who is downright foul when over tired, so there won't ever be anything noisy going on early/late on. We spend Sunday mornings at DS's swimming lessons (OH comes with on the rare Sundays he has off), so there will always be the best part, if not all of Sundays quiet which will hopefully soften the blow of any other inconvenience.
A lot of the jobs are internal works, so moving the boiler should only cause noise on next door's landing while we remove it from the bedroom, then it's going on an external wall downstairs. The kitchen doesn't join with either side, and there isn't one in at the moment to rip out, so that will both reduce noise and mess, and speed up that job.
The big one that is going to create mess and noise is cutting down the tree in the front garden, and cutting back the ones in the back garden. The ones in the back garden side onto an alleyway shared just with us and the rental house next door, so there shouldn't be any issues with us kicking those back into a reasonable size and shape. I don't foresee issues with chopping down the one in the front, it's almost entirely obstructing one of next door's bedroom windows (opposite side, owner occupied) completely covering one of our bedroom windows (literally touching the glass), and it makes the front room like a cave when by rights it should be a lovely bright room. I should imagine they'll be glad to be rid of it to be honest. If they have significant objections, we can top and vigorously prune it, but I'd be VERY surprised if they mind. It's so out of hand we thought it may be protected, but it's definitely not, we checked all of the things we planned to do with the relevant council department before we put an offer in.
The conservatory will only be 3ft by 2.5ft, and only backs on to the side alleyway of their house, so won't even be near their garden. We could do with taking one fence panel out for one day while we render the blockwork which will be on that side, which isn't strictly necessary, so if they REALLY can't cope with it down for a day, we can leave it, as it won't be visible unless you peer through the gaps in the fence, and will be sealed and damp proofed on the inside.
We'll know the month in advance when we'll be doing bits when OH gets his rota, so there's time to shift plans if they have something significant going on we can try to fit around them as best we can.
I'm also planning a home birth, so hoping I manage as quietly as I did with DS or there may be real grounds for complaints going on here! 
I'm on good terms with my current neighbours on the whole (anyone who saw my previous posts about my current next door neighbours will know there's an exception, but they have the full street demented sometimes, so I don't count them), I'd like to be that way in the new place too. We've chosen a property we can develop in the future if we need more space, and hope to be there for many years to come, the last thing we want is starting a chew with the neighbours as soon as we get there. The conservatory is going to be a play room, so with any luck, their children will be able to enjoy it with us when we get it finished. DS is a sociable little thing, so I'd like to build bridges if we can.