Yes.

You need to know what A/C are you using, Non-Inverter? Inverter? And the brand of inverter because some inverter use thicker copper than other, some use 4 wires, some use 5 wires.

You no need to know this, unless you want to DIY.
Even if you want to DIY, you need to have the manual in place.
the number 4 or 5 is more on the controller wire.

Know the brand you want and ask how many wires required. Some need 2 some need 1 for signal.

Why need to go full conceal? You are looking for trouble later on, especially when you want to change brand.
Conceal a PVC pipe for wiring and air cond copper pipe are the best way, so you no need to worry.
If your renovation works not done, suggest to spend some extra money to redo this.
Basic type air cond only 3 wires, inverter are 4 or 5 wires. And air cond installation should be done by air con man, not your contractor do everything first.

If this is the case, you shall not conceal and reroute the air cond pipes.
It may not look good in some sense, but when problem comes, you will know the pain of hacking, it will be very messy.

Nope, you need to install such that both the units are as near as possible. With this way you can hack the wall with a hole, put PVC pipe, conceal back that PVC pipe.
Then the pipe and wiring will be covered by both of the units.
Later I show you my house's photo on both of the installation method.

[attachmentid=4184134][attachmentid=4184135]
This is my room's air cond setup.

On my first photo, that's my master bed room setup, you will see the white hose part, that's the water outlet while the black part is the connection point to the outdoor unit. Those are the parts which will be removed for servicing.
So you need to make sure this part can easily being access.
My PVC hole won't be covered by anything.

Outside, inside also the same.
Insect unlikely to enter since we already blocked it with paper.
As for rain water also unlikely since it is covered by roof, chances of getting rain water are quite low.

Nothing to do with landed or not landed, you just need to plan properly.

You can use plaster ceiling sides to cover the piping.
Looks like normal non inverter