Brora
Rutabaga in the US

Rutabaga are a cool season crop, so you can sow 'em direct in the ground when the soil warms up a bit after the last frost, or even later for a fall harvest. To be honest, they're not usually sold as plug plants, so direct sowing is generally the way to go. Sow seeds about half an inch (1 cm) deep, leaving an inch or two (2-5 cm) between them in rows spaced about 18 inches (45 cm) apart. Once they're up, thin them out to stand about 6-8 inches (15-20 cm) apart. You can sow from May right through to October in some warmer zones, just check your USDA zone for the best timings, ensuring they get about 95 days to mature before it gets too hot or too cold.

Like I said, you mostly sow these direct, so there's not much faffing about with pricking out. If you do start them off indoors, get 'em hardened off proper, a week or so outside in a sheltered spot, before planting out after the last frost. They don't need any support, just room to grow their big roots. Give each plant about 6-8 inches (15-20 cm) space in the row, and they'll be happy. They like a good open spot on the plot, where they can really spread out.