we usually plant anything up to five seeds per space on a seedling tray - some will take, some won't - when they've taking, you can pluck the smaller, less healthy ones out, or you can simply split them like you do seedlings from bunnings. we get the trays for $2 from bunnings - they've got about 15 seedling spots on them from memory - about 30cm square. so easy to use. we have a proper little greenhouse cos DH wants to grow roses from cuttings - it's awesome and cost about $30 from bunnings. just a little portable one
we put all seeds and seedlings in there while we get to them - can't always go shopping and plant same day around here...