Try starting seeds hydroponically. A few links These notes were taken as I watched video of the basics of managing a greenhouse growing tomatoes hydroponically. Even though the focus is on commercial hydroponics, most of the information is applicable to growing tomatoes in soil or potting mix as well. Best orientation for greenhouse is to have the length of it running north to south. Plants will get light from both sides.
Plants grow when their needs are met.
The nutrient mixture water reservoir need not be an expensive tank. It could be a wooden box lined with swimming pool liner material. Perlite also considered good. Vermiculite has high nutrient-containing ability. Lower stems as plant matures.