Colin, great to have you join in the fun, insane at times but still fun.
Your 250 plant grow-out seems a bit meager and small. With all that land it could be increased 10-fold with land to spare. Of course you will have little to no free time growing 250 plants and you will barely be able to make it to your day job in the mornings, assuming you are not retired.
If you are allowing 12 week's before planting outside that is a bit too long. Either plan on planting earlier or starting later. Allow about 8 weeks before planting outside. All joking aside about the number of plants to grow, consider germinating and planting in stages. For example, what date do you think will be the best, most optimal time to plant?
Look around the site for the optimal way to provide heat and light to your young, germinated seedlings. 8 weeks from germination to planting outside will be OK with the right amount of light and warmth for your seedlings.
Considering the area where you live, I know there are times when a system blows in from the Tasmanian Sea and the air can get a bit damp, cool and wet for many days across the entire island. So, be certain that you take steps to prevent your harvested tobacco leaf from molding as it is being cured and dried down if cool, damp weather moves in for a few days.
Overall, you have no worries, there are other people here that are eager to give you advice. You will do very well.