How far apart should I get Fraxel and Excel V laser resurfacing treatments?

Fraxel is a type of laser resurfacing that influences collagen production.  Excel V is a vascular laser reducing redness.    While these 2 treatments can actually be performed on the same date, there is some possible increased redness and swelling, hence, modest increased downtime.   When alternating these treatments there is less social downtime so treatment timing can be customized per patient.

This is correct.  The two lasers have different skin targets, different depth of penetration.  Two weeks in between should allow enough healing to alternate lasers.  

It is not necessary to space them apart. I routinely do them simultaneously. There might be a bit more swelling but the skin can tolerate both lasers. In fact, I sometimes add a QS laser for the darker pigmented areas as well. Using a LLLT such as Healite afterwards will bring the recovery time down. Sleep upright as well.

The plan your dermatologist has laid out for you is a nice plan. Though I dont offer fraxel (I offer Halo which is a newer and more dynamic fractionated resurfacing technology with low downtime) I will often mix Excel V treatments with Halo. I even do them on the same day. As I am sure you have noticed, there is a bit of swelling that can occur with the Excel V, aligning them on the same day can often combine the downtimes of the procedures so that you aren't constantly looking like you have had something done during your treatment course. This is something for you and your dermatologist to explore and see if it may be a good plan for you. Otherwise, interspersing the treatments is an excellent plan and will certainly help you get great results.