Not sure what you mean by saying you will be renting through David's at 7 months out. You should not wait until that time to contact David's. You should contact David's well in advance so it knows it will need to try to reserve at exactly 7 months out.
For the time you want, starting March 5 and days after, the following studios from ones you list are highly likely (close to 100% chance) to be open at 7 months out: Poly, AKV standard or savanna view, BWV pool/garden view (for the last three years, those have all been open at 7 months out for that time of year). There is also some low chance for boardwalk view; BCV is about a 50/50 chance. The only real issue is David's having an owner with the points to make a reservation and, if you are talking about reserving 7 months out, the chances are high.
DVC reservations do not get daily room service-- you get a change of towels, emptying of trash and replenshment of toiletries of your fourth day (and to get to four count arrival day as one) if you reserve 7 nights or less. If you reserve 8 nights or more you get full cleaning service on that fourth day and the trash and towel service on the eighth day. Note if you actually want full cleaning service on any day while there, you can call housekeeping and ask for it (at least one day in advance) but there is a fee ($30 for a studio).
If you have any particular room requests, such as for a room in a particular area of the resort, it is best to ask the owner (through David's) to make the request through Member Services -- you can make far more kinds of requests that way than waiting for online check-in at 60 days out and using the request page during that check-in (those online request pages were created for cash paying guests not DVC, do not cover many things a member can request through Member Services, and many of them are ridiculous in relation to DVC, e.g., at AKV Jambo, you can request higher or lower floor with that online request page but that is a useless request for DVC because all DVC rooms are on the top fifth floor (sixth if club level); at AKV Kidani, you can request near an elevator with the online request page, but since there are three elevators along each wing, that request can be met by putting you in any room in the resort and essentially accomplishes nothing).
Just like a regular Disney cash reservation, you will get a reservation number that will allow you to set up everything for the trip in MyDisneyExperience.com, including adding park tickets and fast passes. If you want to purchase a
Disney Dining Plan, the only way to do so with a DVC reservation is through the owner who contacts Member Services and that reservation for a dining plan needs to be made and paid for at least 48 hours before you arrive.