There are plenty of us on this forum, and if you search the forum you'll find quite a few people asking the same questions.
First of all, yes, it is a money pit. It's also a time pit. It's quite amazing how much of a money pit it is. Owning a listed 400 year old building is essentially an expensive hobby. You do it instead of spending your time and your money on something else, such as fast cars and nice clothes.
If you go into it with your eyes open, you're okay most of the time. If you don't, it's miserable. It's miserable at times even if you think you had your eyes open when you bought it. (When people come up to you after church and tell you that they're praying for you over your house repairs, you know things are bad.)
The things I hadn't anticipated - you have much less choice of tradesmen to do the traditional repair work. You can find yourself phoning people 100 miles away and trying to coax them to come out and quote. You also are very weather dependent - our neighbours have quite literally built a new house in the time it's taken for us to wait for the weather to be good enough to resume restoration works.
On the plus side, you're worrying a bit too much about listed building consent. You need that for touching the structure of the building and anything that relates to the character of the building. So we need to use cast iron guttering (hugely expensive) rather than plastic gutters, we need to repair with proper aged oak timbers, appropriate bricks, appropriate roof tiles and lime plaster, we can't swap our windows for double glazed windows, etc. However, I can paint it whatever colour I like inside, I can put in a new kitchen, and we were able to take down modern dividing walls and put up new dividing walls where we wanted them. However, you have to apply for listed building consent (free) each time you do that.
If you want to PM me a link to the house you're looking at, I'll give my uninformed opinion!