Hinged flaps...again!

Welcome!

Cannot help with the ballasting, as I don't know this product. If you are going to have a lifting flap, then everything on it needs to be
firmly attached.

Alternative suggestion. I was about to build in a lifting access bridge to future proof my layout for older age use; at present it relies on a
'duck-under'. But I am avoiding that, by instead using a wheelchair to 'scoot' under. We got the one I plan to use for our elders, very
cheap at a disability centre, an NHS chuck out because it had no parking brakes and was thus not of the required standard. (We bought
a better one for our elders too, having discovered by experience that the lack of a parking brake can be trying, because the real world
has gradients and people already wobbly on their feet have a profound liking for stable support.)

If you are set on a lifting flap:

The hinge centre line needs to be centred slightly above rail top.
Build flap, lay track across and fix down, cut through rails,
Rail ends soldered to the heads of brass screws is a good plan for long term robustness.
Don't have trailing wires to power the flap rails. Brass slide bolt to lock the flap in position and make the electrical connection between
the rest of the layout and the flap. (Easiest with DC common return or DCC power bus.)
You can go further and use a second sliding bolt toisolate the rails leading to the gaping void, to avoid a train plunging off the edge.

All the best and keep asking questions!

The working principle is very simple.

The sliding bolt is used as an interlocking switch. When engaged in the metal collar the flap is secured in the correct running position. An
electrical connection to one of the rails on the flap is made via the bolt to the collar and can only occur when the flap is secured in the
running position. (Your choice of where bolt and collar go, my preference bolt on fixed side, collar on flap.)

Further elaboration, isolating electrical supply to the layout. Route the supply to the layout through the first bolt. Install a second slide
bolt securing the flap closed, and take the rail supply through this and connect to the remainder of the layout. Either bolt withdrawn cuts
power to the layout, no chance of anything going over the edge, or running into the raised flap.

What about power to the other rail on the flap? You have permanent connections in the form of the hinges, so make those connections
through the hinges. No wires flapping about.

It does cost a little money because what is required for best results are brass bolts and hinges, for their superior conductivity. To do this
with just two bolts if there is more than one track crossing the flap requires use of either DC wired common return, or DCC.

The isolation can all be done with sensors and electronics, but those will not solve the problem of reliable rail alignment, may as well use
the necessary physical components for that, that's value engineering.