Personal experience — the limit (!) 3 projects a day, 6 days a week. Normal load — 2 project. Minimum 1 project. More than three projects do not take (not physically uspevaete).
SN is higher than that specified in the topic... But I'm working on.
Actually, I wrote how to work in terms of contingencies — https://idzenski.ru/kak-stat-dzhiedaiem-dzhiedaisk...
But I recommend you find another office — 180$ for the competent designer a little critical.