Yes, you need to do them one day at a time. Don't worry if you don't get something, people often drop reservations and you might be able to pick one up before your trip.
Oga's has a walk-up list so you could do that on your park day if you don't get that reservation.
You could also set up a dining alert.
As goofy1954 mentioned, hotel guests have often been able to start reserving earlier than 6am PST. I'm staying at the Grand Californian in May, and when I booked ADRs for our trip, reservations opened up for me at 5:40am PST instead of 6. I was able to get everything I wanted that way.
Of the 3 you mentioned, Oga's will most likely book up first, followed by Blue Bayou and then Lamplight Lounge. So I'd try for Oga's first. Sometimes I use my computer and my phone to book two ADRs at the same time.