If it is your dream.....go view, if it is right then the house will tell you so the moment you walk in, it will wrap its arms around you, welcome you and tell you so! It sounds like my cottage - very unspoilt, even down to the original brick floor in the kitchen, well under the downstairs bathroom floor for water etc - what does it have? Character, quirkiness and uniqueness which can never be replicated in some ghastly boxy new build monstosity, which will probably fall down in fifty years because of poor build quality, despite the 'cannot do without luxuries' of central heating, mains drainage etc.
The cons sound minimal - I fail to understand why a septic tank is regarded as a gift from Lucifer - looked after properly they are not an issue. I have one currently, no problems. My last house had one and I NEVER had to have it emptied in 31 years! Yes, you may need to invest in a set of drain rods and spend an hour or so clearing blockages in the foul drain run every now and again, but, so what?
A large garden is wonderful, why should it be a negative? Unless you want to bring suburbia to the countryside with decking (ugh), close boarded fences (ugh), dreadful bedding plants in regimented rows ( double ugh) and hedges manicured to within an inch of their lives ( which should not even be cut between March and August because of nesting birds) - in which case, yes, there would be a good deal of upkeep. A large country garden does not have to be time consuming, onerous or require bringing someone 'in' to do it for you. Let it be semi natural and a home for wildlife - room for veg plots, herb gardens, chickens ( you will have no neighbours to moan about crowing cockerels....in fact you could keep even noisier livestock like guinea fowl, which lay the most delicious eggs, or even peafowl if you had a mind to! And bees....! The possibilities are endless.
No central heating.....so what? Strangely enough, only fifty years ago, very few people had central heating! There is a marvellous invention known as clothing, which, I believe, if worn in suitable layers is designed to keep the body warm. Augment that with open fires or (whisper it, as they are un PC) a woodburner and you are well away.
My siblings and I were brought up in a house which had no central heating - in fact, no mains electricity until the late 1970's - I still remember gas lights popping and fizzing away in the kitchen and living room. There was no road access, one had to walk half a mile along a river bank to get to the property, we walked or cycled to school using those appendages known as legs which we evolved with. You know what, we loved it, helping my dad with his bees, helping grow vegetables, mowing the grass, creosoting the chicken houses, collecting eggs ....I could go on. It was fun, we had fun, we made fun and, into the bargain, we learned an appreciation for and love of the natural world and everything in it. We learned to live with mice, spiders, ants, bats, wasps and other insects, all of which seem to throw most people into a histrionic hissy fit. And, guess what, we are all still alive to tell the tale.
No near neighbours for two miles? Bonus! Emergency situation? That is what telephones are for and, contrary to the general consensus on MN, rural people are actually very friendly and helpful, or at least in my experience, that is so. Lo and behold, most country towns also have something called retail outlets where one can buy 'things' such as food, milk, newspapers and other neccessary goods. They also have museums, theatres and other places of 'culture', along with the requisite coffee shops and gyms, which seem to be the yardstick for defining 'civilisation' in the urbancentric world we now live in.
Do it, buy your dream house, lie in bed at night, curtains open, watching the moon's transit across the sky, looking at stars, unimpeded by light pollution, listen to the owls, foxes and nightlife, unhampered by traffic noise! Do it. Do it!
You sound young - you have your whole life ahead of you to make this dream house what you want it to be. Do it.
Good luck, I sincerely hope you are able to make the right decision for you, your family and any children you have who will know the joy of growing up in a natural, rather than a virtual environment. Do it!!!