Its a big job.. You need floor, insulation, weeping tile or guaranteed drainage, to prevent mold, finished wall and ceiling. HVAC system, electric sub panel, sound proofing, drainage for washroom, kitchen, etc... Windows, and will end up with modest rent for lowish ceiling.
You may be better off renting a spare room in your home and using the crawl space for your own use like laundry, workshop, office, etc.