You're my BW 'twin'! DS here is nearly 14 weeks and I have a slightly younger but non-napping DD 2y8m
fun isn't it!
I have also been wondering about aiming for a longer lunchtime nap with shorter naps either side as I agree that does work better with an older LO and getting out and about. I think your possible routine looks ok but you may find LO is too tired after two short naps to do a good long nap in the afternoon, so perhaps a long lunchtime nap would be better? The thing I've found with DD is that quiet time can be flexible if she's not sleeping, so you could just have her doing that once you've got DS down rather than trying to fit DSs routine around her iyswim?
I guess the thing to bear in mind is BW principles - respect for your LO, following cues ie not keeping a tired LO awake to keep to a schedule, but combining that with possibly a bit more structure to fit the needs of the family. So perhaps that might eventually be a relatively set first nap and waking by 9.45/10am, but then say adjusting nap 2 based on how the morning went and then being a bit more flexible about a CN and BT.
I'm thinking of it as a bit of a 'work in progress'. My feeling is before 5/6 months anyway being too set about timings will probably get a bit messy. But would be very interested to know what you think!