Currently with 2 live-in partners, a girlfriend we see several times a month for a few days at a time and some occasional FWB.
For me, live-in partners and FWBs fit my life best. The "girlfriend", who has her own place (with her husband), is new for me...requires scheduling and compromise, especially as she is also seeing my two live-in partners, so we have to schedule "alone" time as well.
2-3 "serious" interests seems to be a practical limit in terms of day-to-day time...but I would be open to more casual FWBs (where we get together once a month or less, as time provides).
A major limit for me - I don't really like anything other than FTF interactions - I don't do phone very well, although I can do a few txts a day as long as we aren't trying to have a real conversation. So any "occasional" person would have to be ok with long stretches without contact.
On the other hand I am, and always have been, completely satisfied with my life the way it is. Never "looking" but always "open" to new situations...things have a way of working themselves out...
PS. It probably helps, scheduling-wise, that I don't have kids or too many "other friends" that are vying for my time. My work takes up the vast majority of my "not-home" time.