There's no performance problem or appearance problem (in the air) with slits in the covering. If you're concerned about appearance to curious onlookers in the pits, then you need to plot out exactly where the cables will travel through the fuselage sides as you go from one extreme throw to the other, then cut slots in balsa sheeting, or frame slots when you're building. Make them nice and straight, and turn the covering into the slot when you cover. I use a big old-fashioned drafting board to do these plots.

I've never had slit covering tear open on me, but I suppose it could happen. It would take more than aerodynamic stress, I think, to cause a tear. The covering will flex quite a lot before it tears.

Crossed cables take shorter exit slots than un-crossed.

On occasion I get a little fancy and do nice exit slots, but I have a lot more fun when I just slit the covering and go fly.

Another thing I've done many times (up to 60 size, maybe 90 size), but never see anyone else doing it, is run nyrod back to the rudder in pull/pull configuration. You can use outer nyrod guides, braced every 6" or so, and then you don't need to have taut cables. The inner nyrod will flex through a fixed exit in the fuselage and bend in or out as the rudder moves. You can glass over or cover over an outer nyrod guide which has been sanded down to the contour of the sheeted fuselage, and have a very clean appearance when you're done.

There's really no issue with the inner nyrod distorting under compression, since it's the pull side that does all the work, while whatever stiffness there is on the push side can only help balance the load on the servo output shaft. Terminal linkage is very simple when you use nyrod.