This starship class has been slowly coming together in my mind for years. I will try to address all the comments that have been made so far in this post. If you're looking for pretty pictures first, links are at the end of this post.
Cary L. Brown, the Endeavour is meant to be a contemporary of Enterprise 1701A. Below is the description of the ship given on the "Overview" section of the plans. This is as good a place to start as any:
"The Explorer class cruiser is a medium-sized starship. All vessels in this class are named after early Terran exploration vessels. The design of this class is an indirect descendant of the original MK-VII Hermes class scout. There have been numerous design improvements over the years, including an enlarged engineering section and upgraded defensive systems.
"The primary mission of this starship is long-range exploration. This vessel is designed to push back the frontiers of the Federation, gaining knowledge and scientific data as it progresses. To this end, the Explorer class starship is equipped with a wide variety of research facilities, from traditional laboratories to holographic simulators, where virtually any environment or set of conditions can be duplicated.
"This ship is also equipped with two of the new WR-07A Powell class warpshuttles. These vessels, recently introduced into the fleet, are similar to large shuttlecraft, with two major exceptions: They can be self-sustaining for months at a time, and they are capable of speeds approaching warp four. With these warpshuttles, a starship is no longer tied to a newly discovered planetary system for extended periods. A research team can be left in a warpshuttle to explore the system in depth, then rendezvous with the mothership research and data-gathering activities are concluded.
"Sad experience has taught us that, peaceful though our intentions may be, the universe at large does not share that sentiment. Therefore, every ship of the line has at least one detachment of Starfleet Marines assigned to it. In the case of the Explorer class, their facilities are housed in the secondary hull."
I will cover further details and my design reasoning further down.
Mysterion, Here is the crew breakdown:
COMMAND:
COMMANDING OFFICER (CPT) 1
EXECUTIVE OFFICER (LTCDR) 1
HELMSMAN (LT) 6
YEOMAN (ENS) 2
CHIEF NAVIGATOR (LTCDR) 1
NAVIGATION OFFICER (LT) 6
ORDNANCE OFFICER (LT) 3
ORDNANCE SPECIALIST (ENL) 18
TOTAL 38
SCIENCES:
SCIENCE OFFICER (LTCDR) 1
ASST. SCIENCE OFFICER (LT) 1
SCIENTIST (ENS) 6
LABORATORY TECHNICIAN (ENL) 72
CHIEF SURGEON (LTCDR) 1
DOCTOR (LTCDR) 3
HEAD NURSE (LT) 1
NURSE (ENS) 21
MEDICAL TECHNICIAN (ENL) 30
TOTAL 136
ENGINEERING/OTHER:
CHIEF ENGINEER (LTCDR) 1
ASST. CHIEF ENGINEER (LT) 1
ENGINEERING OFFICER (ENS) 4
ENGINEERING SPECIALIST (ENL) 28
TRANSPORTER SPECIALIST (ENL) 15
CHIEF OF COMMUNICATIONS (LTCDR) 1
COMMUNICATIONS OFFICER (ENS) 5
COMMUNICATIONS SPECIALIST (ENL) 11
CHIEF OF SECURITY (LTCDR) 1
SECURITY OFFICER (ENS) 5
SECURITY SPECIALIST (ENL) 30
TOTAL 106
STARFLEET MARINE DETACHMENT - SEE SFM PUBLICATION M11768-4B FOR TO&E
TOTAL 25
THE STANDARD SHIP‘S COMPLEMENT IS 76 OFFICERS, 204 CREW MEMBERS AND 25 MARINES TOTAL 305
IN EVERY CASE MINIMUM GRADES ARE SHOWN FOR EACH BILLET. INDIVIDUAL SHIPS MAY VARY
BY REASON OF INDIVIDUAL MODIFICATION.
Albertese, The Explorer class starship is equipped with 12 phaser turrets - significantly fewer than Enterprise. I'm not sure what led you to believe there are more. Please elaborate.
BillJ and Wingsley, Cary L. Brown's comment about warp nacelle placement sounds like a good explanation to me. The truth is, they're where they are because I like them that way.
Winglsey, the navigational deflector is on the bottom front of the primary hull. Not very visible from the side, but very much so in the bottom plan view.
SonicRanger, I've looked at this design for years, and didn't see a dick on the ship 'til your comment!

It's ironic that you mention those particular aircraft; I chose that color for the front of the secondary hull as an homage to that era's jet aircraft. The front houses the space/planetary sensor array, and thus needs to be "transparent to electromagnetic energy," the same as the radar domes you refer to on the F4 and A7.
I was somewhat worried about blocking the lower primary hull array with secondary hull as well, thus my reasoning for locating the SPSA at the front of that hull. There are also sensors around approximately 75% of the primary hull, as well as on the aft edge of the upper and lower dorsal. This baby is loaded to the TEETH with sensor capability.
Herkimer Jitty, that is a good idea. I think the unofficial Starfleet nickname for Endeavour will be "Biggus Dickus."
Kaiser and Mysterion, and anyone else interested in a set of plans or the manual: The plans are finished, and are available in 11x17 format ($20.00+shipping) or 24x36 format (in scale with the FJ Enterprise plans)($45.00+shipping). They both are comprised of 14 sheets, consisting of 5 exterior views, an interior cross-section, and detailed deck-by-deck plans. Schematics are also included for the WS-07A Warpshuttle, as well as all of the smaller support vehicles aboard (lifeboats, shuttles, work bees, etc.). What is currently available, though, are only in black & white. I'm working on converting them to color, but it's taking longer than I expected. Color will increase the cost somewhat as well.
I am currently working on the Crew Orientation Manual in parallel with other ongoing projects. I hope to have it done within a year. With any luck it will be a lot sooner. I'll cover the content of that in more detail at a later date.
ALSO, if anyone would be interested in modeling this design for me in 3D, I would be willing to pay for the service, if within my resources. If this is you, please let me know.
Finally, Here are some links to a few hi-res views of the ship. I apologize if the watermarks obscure too much detail; I trust that you'll understand.
Side Elevation:
http://starshipdynamics.com/download/01-Endeavour_side_view.jpg
Top Plan View:
http://starshipdynamics.com/download/02-Endeavour_plan_view.jpg
Bottom Plan View:
http://starshipdynamics.com/download/03-Endeavour_bottom_view.jpg
Front / Rear Elevation:
http://starshipdynamics.com/download/04-Endeavour_front-n-rear_view.jpg
Cross-section detail (still a work-in-progress color-wise):
http://starshipdynamics.com/download/x-section_detail.jpg
And, as a bit of a tease, a detail of one of the deck plan sheets, so you can see the kind of detail I like:
http://starshipdynamics.com/download/deck_plan_detail.jpg
Enjoy! Thank you so much for your kind words and comments. Please keep them coming. I'm hoping that y'all can help me keep my creative juices flowing.
If you're interested in further info, or details on other plans that I've done, please check out my Facebook page at
http://www.facebook.com/starship.dynamics. Feel free to "Like" the page if you want to keep up with new additions there.
I also have a webpage at
www.starshipdynamics.com, but it's still very much under construction at the moment.