Stepping the mast (and setting up the rig)
2kUS for a mast would be unaffordable for me, but if you can get a carbon fibre mast - good - that's the best for a number of reasons. Whether you can easily raise and lift it with all its masthead running rigging in place (as it would be), keep it vertical and thread it down through the partners all the way to the keel step is not a trivial exercise for a mast that length. Will you be standing alongside the dinghy (on its trailer) while you do it? (I've seen it done that way, on a Paradox, but I wouldn't be able to do it). Or will you be doing it from up on the deck, presumably with the boat still on its trailer? (I'd get vertigo).
I think these are matters which you can figure out later and are perhaps not crucial to decide at this stage, but you might mull over ways of stepping the mast.
Things to think about while enjoying the Christmas festivities.
I dare say you are younger than me, but don't write off the idea of some kind of tabernacle.
And then you've got the task of setting up the sail bundle each time you launch the boat. Use clip-on standing parrels I suppose, and try to keep the sheetlets/mainsheet spaghetti tidy and untangled.
The very simplest kind of dinghy "tabernacle", which I think (when I get a round tuit) I might try on my Golden Bay dinghy, with its somewhat shorter mast , is a simple over-diameter tubular housing which stays permanently in place and sticks up above the deck as high as necessary (even above the normal level of the boom, if necessary to clear a cuddy), into which a light mast can be simply slid down - that is, if the mast is manageable enough to be lifted and held vertical long enough to get it in and started. It won't make raising the mast much easier, but I have the idea that the furled sail bundle (which otherwise would be somewhat time-consuming to set up each time) can be left in place permanently in its parrels on that stumpy "tabernacle" tube - also with sheetlets and mainsheet already rove. Then all that would be needed to go sailing is to drop the mast in and lock it (already dressed with its masthead running rigging), clip on the halyard and standing lifts - and you're ready to raise sail and go. As near as you could get to the situation on a moored boat. I've never seen it done. [Edit: in a later post, Arne has suggested the same idea with his "Tube type mast socket", and also confirmed that the mast will be light enough to plonk in place. In that case I think this is definitely the best kind of tabernacle for a dinghy. Managing the sail bundle that way, with all its sticks and string, will be a godsend. Make sure the mast locks in place when dropped into the tube, so it can't rotate. Junk rig imposes rotational forces on the mast which may be inconvenient.]
A conventional forward-opening tabernacle would probably set the rig too high above the cuddy, (as you have already observed) unless you cut some sort of trunk or case into the deck to allow the heel of the mast to swing down below deck level. That's all too much trouble and time to be worthwhile, probably, on your boat, and I don't suggest it. (And, by the way, you wouldn't want the kind where a pin goes through the mast. That's a weakness at the weakest point. The pin abaft the mast is better, in a free-standing rig. For a small dinghy I would put the pin through the tabernacle itself, just aft of the mast - and use a square lashing for the hinge. Never seen it done, but I can't see what would be wrong with a rope lashing, for a dinghy).
There is a type of hinge arrangement which has a sliding outer tube which slides down over the tubular internally-hinged mast, when the mast is up. Personally I don't like that idea at all, but evidently it does work.
For a camper cruiser I still like my "hingeless" heel hinge in which the mast is stood up from the heel and into the partners then locked in place with a gate at the partners. Much easier than picking it up bodily and trying to drop it down through a hole in the deck. But that only works if the cabin top is open. The open top in itself has other advantages in a dinghy, and a removeable canvas top (or quick clip-on canopy) is not too difficult to make. Well, I've thrashed that idea already, but since you intend to modify the cuddy top, I mention it again and suggest consider it.
(The first of the two main advantages of the junk rig is: incredibly simple reefing and handing, especially when single handed, and you can raise sail, hand, reef or unreef without even having to be head to wind. You don't even have to stop the boat to do it. But the downside is - the "price you pay" - the rig is a bit more complicated to set up initially, ideally suited to being permanently set up on a moored boat and not so ideal if it needs to be dismantled and re-assembled at each outing. There's ways of speeding things up, I've got mine reasonably quick now.
One day maybe someone will start a thread on easy mast raising and super-fast ways of setting up a junk rig, for trailer boats, as there seems to be a bit of a trend these days towards smaller, trailerable sailboats.).
Ballast would be helpful, even if minimal, better than none. Perhaps, especially in the deeper-bodied narrow-on-the-waterline type of boat that is designed for it - less so for yours I think - you might find you have enough weight already without ballast, but maybe you can keep the option of trying it. As an alternative to pumping and discharging seawater, and much easier to fit than making water ballast tanks, I have considered packing bags of wet sand (off the beach, and leaving it behind afterwards). Wet sand would be a bit more effective than water, as ballast. And that way you could try a bit of ballast in your boat and see how it works out, without having to commit to any major modification. Would just need to be lidded down and secured under the floorboards, along with your water bottles, tins of balked beans, cans of beer etc). Again, never seen it done. More things to think about later.