You can book only 7 nights when reserving exactly 11 (at home resort) or 7 (at others) months out. If you actually wait to reserve beyond that time you can reserve more, actual restriction is that your departure date from WDW can never be more than 11 (or 7) months plus 7 days from date of making a reservation. For example, if you reserve at 10 months out from date of arrival, you can book 30 days at a time.
If booking exactly 11 months from arrival date and you want more nights, and you are still using same use year, then you should modify by contacting MS (or using the modification tool online) every fews or more days (if you booked 7 nights to begin, you can actually wait up to 6 days to book more). If doing a 7 month reservation, you must make changes every day at 8 a.m. to have best chance of getting all the nights you want.
You need to book two separate reservations if you are using two different use years, each of which reservations will have its own start date, e.g., book part of trip with one use year and other part with other use year by making a second reservation 11 (or 7) months out from the designated departure date of your first reservation, and then contact MS to link the reservations.