For Rs.850,000 if you have a choice of vitz and civic so i would choose vitz because civic is on a higher side but on the other hand keeping in view the current market situation civic is also not bad but if you want economical car so ofcouse i would personally recommend you vitz..
As far as your question is about parts so there is no such tension to find parts of vitz or civic.. Your second question about comfort so i dont know about civic but vitz is also a comfortable car because i almost spend my day going around in vitz.. Third question about looks so c'mon you cant compare the looks of a hatchback with a sedan.. Forth question for worth so vitz have more worth.. Last quertion about performance so again you cant compare the performance of a 1.0l engine with a 1.6l engine so i would favour civic for this..
But if you consider your system space requirement so you will have to put those big enclosures on the rear seat in vitz but in civic you will have enough space..
So anyway good luck with your decision..