This post is just relating my experience since the early 70s concerning where I germinate seedlings.
Like many, I started in the basement. Unfortunately, as the number of seedlings grew, so did the odor.
I next went to an attached sunroom. Because of odor, the sliding glass door that connected to the house had to be sealed with caucking and plastic tape. After several seasons I noticed a black mold type problem starting. I had to remove the inside walls, clean everying out, and then put in new walls.
I then moved to shelves in the attached garage. Again, odor started so the door from the garage to the house had to be sealed. Plus, we soon lost the use of having a car inside during the bad winter months (the larger seedlings had to be placed on the floor). Also due to the high humidity mold/rust started on the walls and the inside of the outside garage door.
At this point I should mention that at first I would start germinating seeds soon after thanksgiving. This resulted in having many large potted seedlings by the time it was warm enough to plant outside. I then started moving the “shelling” time back, first to Christmas break (I was a teacher) and then to January. (My experience is that seeds stored in the hips will not germinate.) This year my plan is to start in the middle of February.
I now start the seeds in petri dishes on Bromelaid/water soaked sand in a half sized commercial freezer set to run at its warmest setting (around 50 degrees F.). The freezer has strings of red LEDs in it. This system gave very satifactory germination results last year. The freezer is kept in the garage.
Once a seed germinates, it will be placed in a normal seed tray (watered with 5 ml 3 % drugstore type hydrogen peroxide to every 95 ml of water). The potting soil is a commercial coir - peat moss mixture.
The seed trays will be placed in “4-tier Mini Green Houses” that I have placed against an outside back wall of the house where there are no windows (the units will be facing West). (Our allotment restrictions do not allow permanent separate buildings such as a normal greenhouse.) Essentially these Mini Green Houses are 4 shelf units with each shelf holding 2 standard seedling trays. Each unit comes with a zippered plastic cover. I expect to need three such units. (Thet can be purchased from a number of suppliers on the internet, for example, www.FarmTek.com, item 102445.)
When the seedlings have outgrown the Mini Green House, they will be placed directly into the raised seedlings beds. Initially they will be protected by an opaque plastic gallon milk container which has the bottom cut off.