I am operating under the assumption I need to send six months' worth of bank statements - can my October bank statement work as both in this case (as six months takes me back to August)?
You have to send the most recent 6 months of bank statements and payslips anyway to show your financial situation.
I would imagine you would be able to use one of those bank statements as one of your 6 letters, as long as you made it clear that you were using one of them, but if there is any other letter you can use instead, it might be easier and clearer for the application to do that.
Remember that you need at least 3 different sources of documents, so just make sure you don't have too many bank statements and not enough other sources.
My other options are a paystub from an interview he went on that was dated October, and a jointly addressed letter from our utility company (not a bill - the advice doesn't say whether general letters are okay or not when it comes to utilities). This is literally all we have from that period. Any idea if either of those would be acceptable? (I would suppliment his post with something of mine from the same period.)
I would probably send the utility company letter as well, and if it isn't acceptable, then ask if your October bank statement can be used instead.
2. So, between us, we have four jobs. I have the payslips from his main job (the income from which pops us over the minimum - which I know we don't have to deal with, but it might be relevant to the question), and the payslips from our teaching work at the university as well. But I am missing several months' worth from my retail job. I have ordered them twice from my company's HR department, but they have yet to arrive. I have the odd one, but I have a gap from September-November (and I know I never received my November one). I am going by my store today to see if my manager can find the original behind her cupboard or something, but what happens if none of this materialises? Any advice?
As there is no official minimum income requirement, it is not so important that you need every single document. As long as you can show the most recent 6 months of payslips and bank statements from at least one of you, showing that you have enough money to live on, I don't think it will be a problem.
Just include as many of your retail payslips as you can get hold of, along with his payslips. If you are including your university payslips the retail ones won't be particularly relevant.
3. Also - 'probably want to make copies' is a phrase used in the application. Probably. How many would they like?
Is it used? I've just looked at the application and it says several times:
You should photocopy each of these documents and provide the copies in addition to the originals.Nothing about 'probably making copies' - you HAVE to make copies.
I would send one photocopy of everything you are mailing to them, so that you ensure you get your originals back.
I would also make a copy of everything to keep for yourself while the application is processing, just in case.
4. The application asks how long I have been in the UK. I have been here since September 2006; however, I did go home between late June and late September 2007 between my MA and PhD. Any idea how to write that one down? I will be detailing how it worked in the covering letter, but I'm not sure if I should say 7 years and 4 months, or 6 years and 4 months.
I would give the time between September 2006 and now, as you haven't been absent for more than 6 months in that time - so 7 years and 4 months.
The application then asks for absences of more than 6 months, so you don't need to mention anything about your absence there as it was only for 3 months.
5. The application also asks vaguely amusing questions about how often I see my husband. Uh, we live together. Every now and then we go on conference trips alone, but that's a couple of days at most. Presumably a completely non-snarky (honest!) 'every day' is acceptable?
Yes, 'every day' or 'we live together' is acceptable - that is what they are expecting you to write.
6. And the part about 'significant ties to another country'. My side of the family is still in the US. Am I right in assuming that just saying 'immediate and extended family US citizens/residents' is enough here? Would they like to know the rough proportion of my friends circle that lives there? Names? Addresses? Number of times I've bridesmaided for them? What? 
(I absolutely have no idea how to answer this question in actuality. I have family and friends back home. Of course I do. I have roughly the same number of both here as well.)
Just put 'United States' and 'Immediate and extended family/friends/other ties you have'
As far as I know, no more detail other than that is needed.
Forgot one - the question about 'could you and your partner live together outside the UK'. Technically, yes - but not without considerable change in finances/occupations/etc. I presume 'no' is the correct answer, then?
Yes, you're going to have to answer no, even if it isn't convenient.
They are looking to see whether, if your visa is refused, you can physically live another country, or whether the UK is your only legal option. As you can legally live together in any other EU country, or the US, or you could qualify for visas for a third country, then you can't answer 'yes'.
You would only be able to answer yes here if, for example, you were an asylum seeker for whom it would be life-threateningly dangerous for you to return to your home country and there wasn't any way for you to gain a visa to live in another country.
Or for example, there was some reason why your UK citizen partner cannot leave the UK, or perhaps they have a terminal illness and cannot travel anywhere, or they are not legally allowed to enter the US or any other country.
