It is overwhelming having all that responsibility. Maybe it will help to think that if you do carry on, in just a few months she'll probably be on enough solids to make things a bit less intense (although that somewhat depends on whether you go down the baby-led or puree route)?
I've never understood why people think that formula is more satisfying - honestly - I really don't :). It's harder to digest as it's made for a multi-stomached bovine so babies can sometimes go longer between feeds because their bodies struggle to digest it, but it actually has fewer calories than breastmilk (albeit that the difference is tiny). BUT that's a different matter, and you know all this, I'm not trying to make any points! :)
I love the fact that you've said that you won't let people's being surprised stop you. I fed DS1 to 15 months but at that point only at home. So for me it was hitting a year with DS2 that I needed support with as I was still feeding him quite frequently, including in public, and that was new to me. For someone else it might be 6 weeks, 2 years, 4 years... or a few points over the course of the BFing relationship - often it's when you stop knowing people who have done the same thing, at least in RL. I found that actually there are loads of people feeding for a long time that I know, but until it came up in conversation I'd no idea!
OK, night times. Firstly, if you are having to get up for night feeds then have you looked at bed sharing options? That in itself can make a massive difference. It's something we talk about a lot here and if it's not for you, that's fine, but it would be the first option to consider as your baby almost certainly needs the milk right now, and so getting it into her in the fastest and easiest way makes a lot of sense. It doesn't necessarily mean moving to full time bed sharing. Maybe a couple of times a week - if necessarily just you and your DD, might be enough to give you the extra sleep to make you feel better.
Would it be possible to get to bed really (stupidly) early a couple of nights a week? Say about 7ish? Even one night a week might be enough.
If you don't want to bed-share, what about bringing her into bed for the first couple of hours in the morning? If she's an early riser then she may snuggle up to your boobs and you can drift along - maybe get another hour that way.
Or, on a morning that your DH isn't working, maybe you give her the early morning feed and then he's responsible for her while you get a lie in? This can work really well when she starts having breakfast as he can give her brekkie while you get a well deserved extra hour or two.
There is a page by Dr Sears which covers night weaning although it's written for toddlers of a minimum of 1, preferably older. But it might give you ideas of things to try. www.askdrsears.com/topics/sleep-problems/night-weaning-12-alternatives-all-night-nurser
While there is no doubt that trying to night wean a 5 month old who isn't naturally "sleeping through" is a risky business, there is also no reason why you can't try to get her to sleep longer than 2 hourly. It's not an easy task and for many it's just easier to go with the flow and feed her back to sleep, but if you're getting up for this it will be really tough. It might be worth getting your OH to try to re-settle her. It will be really obvious very quickly whether this is going to work, or whether it's just going to really upset her. if it's not working, just consider trying again in another month or so.
Does any of this seem useful? If not I will put my thinking cap on :)