Hi Hard,
Unlike Arne and Annie, I think this may be a good way to get yourself a junk-rigged voyaging boat. Easier than starting from a pile of aluminium plates and a welding kit, and easier than having to undo, change and correct all the unsatisfactory things you would probably find in a secondhand boat. This appears to be the hull and deck of a good boat, with most of the heavy, dirty work done, and just waiting for someone to build furniture (which can be simple and open-plan, to save time and money) and rig her.
I owned a boat of this size for 16 years and many ocean miles, and I think that 34- 35ft is the right size when you don't know whether you will be sailing alone or as half of a couple. A full-time singlehander ought to choose a smaller boat, maybe around 30ft. A couple would need to live simply with not too many possessions; it can be done, if they are good enough friends and can live in a small space.
I also sailed her under a single sail some of the time, and a ketch rig the rest of the time, so I can comment on that as well. A big single sail of around 600sq ft can be handled by a young, fit, strong sailor, but I would discourage you on the grounds that placed as you are, you would find it a very big challenge to build a rig that is light enough and strong enough, from materials that are likely to be available to you, and obtaining a suitable mast will be a big challenge also. Making a 600 sq ft sail shouldn't be a first project, you need to learn on smaller sails.
I think you should put a two masted rig onto this boat. Looking at the photos, a schooner with a large mainsail seems to present difficulties, with the mainmast being too close to the sloping windows of the raised coachroof. I would guess that a rig with two equal sails might work, but a ketch with a mizzen of say 40% of the total area would be easier to arrange. That would probably put the after mast where you've indicated on your 'schooner' mast position photo, the mainsail would be 360 sq ft and the mizzen would be 240 sq ft - or something close to those figures.
When I was building my last-but-one boat, a four year project, I kept a sailing dinghy that I could take out for an hour or two, just to remind myself that the sea was still there waiting for me, and to get the dust and fumes of building out of my lungs. I recommend taking a little time out like this, occasionally - but not too often. You need to remain very focussed, to make a success of a project of this size. You will have time for just three things in your life - boatbuilding, boatbuilding and boatbuilding.
But to get down to the details, I have to say to you what we usually say to all those who are getting into junk rig with no previous experience - you will need to buy a copy of "Practical Junk Rig" by Blondie Hasler and Jock McLeod, to gain a good basic understanding of the process of designing and building a rig. It can be found on Amazon.