5 rounds are a lot. Ideally, # rounds ~ ceil(log2 # teams). In the last round you'll have the first playing with the bottom, unless you allow replays (then it is Danish, not Swiss). I'd say 3-way, but not sure. A 3-way takes 2 rounds, as each team faces 2 opponents. Not sure how to score. I know you get an IMP diference for each team, my first instinct would be to VP that using same scale but 2x # boards, 16 in this case. I think Danish allows last round replay only.