4 is kind of on the low side for even a server cluster (3-5 machines).
8/12/16 would work, but 4 leave 3 the moment you take one out for an uplink.
8 would work. Leaves 7 for internal use and one for uplink, or a way to handle 7 clusters down and one uplink for external traffic.
But cudos for finally giving us the "Missing link" with a 100g switch - it is definitely an amazing start. I wondered whether you would touch that one and when. Now it is clear - you did. A small only 4 port, but a 100 gigabit switch, finally moving into the area of high performance switches.
THANKS A LOT - those around are insanely expensive and it is good to see a start into this area of the "mikrotik treatment".