I feel like this is a dilemma that everyone here has had or will deal with at some point or another, when I was sowing my sun openers I had an entire field of tiny H. salicifolia seedling sprouting up all at once (half 'how much to sow per area?', half I accidentally dumped a whole bunch into one spot). I would use the germination rate as a guide for how many you'd put into each pot, especially if you're gonna use those small K-cups (cool find). So if the seeds are roughly 50% germination rate, maybe two per cup? If you space them out so each has their own respective 1/2 of the pot, if they both sprout, once they get big enough to transplant they should both survive. It's also completely dependent on the species, some love being crowded, others hate competition. Also another thing you can do if you have enough seeds to spare is to just sow a bunch and then once they geminate 'thin the herd' leaving the bigger and stronger ones to survive to transplant size, so if the germination rate is 50% you could sow 4-6 or however many you want per pot, then you would expect to see 2-3 sprout up, and then you can pick which you want to keep.