The Harken website has great resources for exploring rigging options. I found it a good place to start when we modernized a similar boat recently: Harken Tech Corner
Based on my experience, which is limited to messing with two boats:
1. Rope clutches are working for me. I ran all the lines back to clutches installed just forward of the coach head winch on either side of the companionway.
2. I modernized the deck line organizers that guide the halyards and control lines aft from the mast to the rope clutches.
3. Sorting out the blocks at the base of the mast is a bit of an issue that varies from boat to boat. Want the lines to turn in a orderly fashion from the mast to the deck organizers with the right angles.
4. Boom vangs can attach to booms in a couple of ways. The common ones seem to be a key slot in the bottom of the boom with a complementary key on the top block in the vang, or a bale attached to the boom with a through bolt.
It pays to spend some time scouring the Internet forums for tips and advice on options, one rigging system at a time. There are different ways to rig each system, with advantages and disadvantages.
It pays to walk the docks with a digital camera, taking pictures of rigging on similar boats, and talking to folks who have gone before, and prowling marine store shelves. Take printouts of photos of your boat with you.
It is a good idea to find a competent rigger, to check choices and installation procedures for safety (load limits, angles, attachment methods, etc).
Don't commit to lines coming back to the cockpit on one side or the other until thinking through and trying out different options. After a few sails you might want to switch various lines around at the clutches, for example. Even after the best planning, trial and error sometimes is necessary to get the optimum layout sorted out.
Racing is different from cruising. If you plan to race for fun but mainly cruise, think about the extra demands of racing (safety, layouts). I find that racing for fun helps me set the boat up better for cruising.
Have a good look at the old standing rigging elements to see if any of them need replacement.