Great idea, really love the direction you are taking it.
Few things I could add is: heating expenses can go very high very fast, depending of area, construction quality,heating pipe installation outlay and buildings you share walls with (if there are such). Really hard to predict now theoretically, ideally you would consider all those things :).
Also if you are taking a part time office manager, ideally you could offer the person a place to stay and reduce the salary by X the person would pay as rent anyways, decent tax savings at the end of the year.
The idea for a café/restaurant is great (if you want to serve food you prepare it complicates things greatly though so to be considered, I would opt for a café to start with or outsource the food preparation, sushi or a lot of vegetarian dishes/raw dishes can be easily stored for a day or two). There is a big amount of board game events organised in Brussels for example (and it's a growing market) so things like that can be integrated in a café offer, all you need are tables :).
Also, considering I am paying now more than 1000 euros monthly just for apartment+internet+water/elec/heating, your concept is very interesting for me :).