How to finnish a hole in pasterboard wall?

I have made a hole in a platerboard wall that has the eaves on the other side. This hole was made to house a projector - due to the sloping ceiling and the throw of the projector it was best placed in here. (also can hide it).

I have still to box out the inside of the hole and fit some vent to help with heat build up. I plan to use magnetic catches and fit a panel inside the hole with a hole so the projector can still project its image.

As you can see the exisitng plasterboard has been sanded flat with the uprights, some parts need some plaster as the existing plaster fell off the bonding in some parts. What is the best way to finnish off these edges?

I was thinking of the right angled plastic trim, but could look a bit naff.
I could use metal beading and only plaster up to the beading on the ouside, not inside of the hole?

Thanks
Pody

Fotgot to mention, The room has been lined over the plaster so this will need replaced in this area.

Could I fix up the plaster in the area and paper round the edges into the hole - would thisd give the corner of the plaster enough protection?

I would use a cable access port (or several) of the sort used in office furniture. If you want a bigger door then prefabricated loft hatches might be suitable.

Of more concern is that by breaching the vapour barrier you are allowing warm moist air into the roof construction, risking condensation, mould and rot of the structure.

Oops, the second picture did not appear properly - I've edited the original post.

Is the plasterboard classed as the barrier? I have several access doors in the eaves (with gaps) isnt this the same thing?

Im talking about cutting a sheet of mdf the same size of the hole in the wall, cutting out a circle where the image will pop out. Paint this the same colour as the wall and fit with magnets flush with the wall?

Why not frame if like a door and have some architrave too?