In Rambam, Hilchot Ishut, Chapter 14:1, he outlines a husband's obligations of onah (conjugal rights) to each wife based on his profession. So a sailor every 6 months, an in-town laborer twice per week and so on.
In applying this to a husband with multiple wives, one could say he must satisfy each wife this often, so a sailor with 4 wives must be with each every 6 months, a laborer with each wife twice/week (requiring more than 1 per day somewhere in that week) and so on. Alternatively, one could say he is obligated to provide conjugal rights to some wife this often, but each particular wife less frequently. This would mean that the sailor with 4 wives is only obligated to satisfy each only once in 2 years.
In thinking about clothes and food, clearly more wives mean the husband has more obligation. He can't provide them with the food for 1 wife and say they must share it. Similarly, he can't provide 1 dress and tell the other wives to go nude. This accords with Rambam in halacha 3 there, that he may have additional wives only so long as he can afford them all and doesn't reduce clothes, food, or conjugal rights.
This suggests that the obligation in onah is like the first option above, and a man with 4 wives is obligated in onah 4 times as often as a man with the same profession and 1 wife.
Yet in halacha 4, the Rambam says explicitly that it is like the second option and the husband of 4 wives has the same onah responsibility as the husband of 1, but that obligation is spread and divided between the wives. So a worker with 2 wives is obligated to each weekly (instead of twice/week) and if he had 4 wives, he would be obligated to each only once in 2 weeks.
How does this not contradict halacha 3, that he cannot take wives if it will reduce his food clothing or conjugal duties to the existing wives?