I have one those center line finfer thing,
I just draw the center line hinge line with a straight edge.
using a sharp #11 blade, cut slowly so the blade stays at center as much as center a
possiable. Sometimes the blade will flex can get off center.
Sometimes you might have to rock the blade back and forth
or slide it back and forth.
Sometimes this will create this slices of wood and must be clean out.
I do it by text fitting a hinge in all the slots and pulling it in and out
to clean out the wood.

I make the slots for the control surfaces before beveling. you'll have
to be more careful with the centering.
If you having covered it yet now is a good time to drill tooth picks into them.
You don't have to.
I find it much easier to install the hinges to the control surfaces before covering.
I drill holes at the center of the hinge slots. This will allow glue to seep in if I need
to add glue later.
However, I use Medium CA . This allows me more time to wick the glue into the hinges
and centering posistion of the hinges. I check and pull on the hinges as hard as I can.

When gluing the control surfaces to the wing or stabs(after they're covered), I use epoxy.
This allows me time to get it right . Posistioning the cntrl surfaces making sure
the tips are even and ect . It also allows me more time to makesure all the hinges
are all the way in the TE. No hinges get bunched in the gap line.
Hinge bunched in the gap line would probably cuase flutter, I imagine.
It also allow me to minimize the gap line as much as posisable to minimize posiablities
of flutters.
I don't wipe the eccess epoxy off right away.
Wait until it cured a little bit. It can scrap of with a blade when it's a little bit
spongy. It's claner....trust me.lol

I usually seal the gap line with a strip of flim.
Depending how beveled the control surfaces.
On most of my air planes, it's for maxium throw. Somewhere in the 60-75 degree
I usually flex the the cntrl surface to max throw and iron the film a litte bit
at a time . I usually seal it from the bottom making nice and neat as much as possiable