Wiring to telephone extension sockets

[RobinClay]

This is an old house into which we moved last year.

There was a BIG (36-way) junction box in a bedroom fed by the 8-core BT cable from outside. From this a 41-core cable (X) fed the master socket (well, it's got a condenser) in the kitchen, from where a short length of six-core (Y) was connected to another piece of 41-core (Z) that runs outside the house, then back in again, to the sitting room and bedroom - I guess, since the telephone sockets in those rooms work, and didn't when OpenReach disconnected the BIG junction box. I guess, when this was a business premises ten years ago, they must have had a swichboard.

OpenReach came at our request, and removed the junction box, and replaced it with a new master socket, with A & B terminals connected to two cores of the incoming BT cable.

The new master socket has only three "out" terminals, 2,3 & 5, and only two cores of the 41-core cable (X) are connected, to terminals 2 & 5.

Down in the kitchen, the old master socket is still there.

Q.1) Is this O.K. ?
Q.2) Can I remove this old master socket, and replace it with a junction box under the floor (we don't need a socket in the kitchen) ?

At the moment, the old master socket in the kitchen has 6 terminals, with "in" connections to 2 and 5, and "out" connections to 2, 3, 4 & 5
That short length of 6-core (Y) has all six cores connected to various strands of the 41-core cable (Z), though the two "spares" are not connected to terminals 1 & 6.

I have bought a length of standard 6-core cable.

I aim to remove cable X and run a new cable (M1) from the new master socket to the junction box and thence (cable M2) to a new extension socket in the dining room, and re-connect the other existing 41-core cable (Z) at that junction box, so that the other sockets still work.

My inclination is to connect the appropriate cores in cable M1 to the three terminals 2,3 & 5 in the new master socket, and then in the junction box connect all six cores in cable M1 to both cable M2 and to the currently connected cores in cable Z.

Q.3) Can I use an ordinary "chocolate bar" connector as a 6-way junction box ?
Q.4) Should I wrap it in insulating tape, or can I just leave it exposed (under the floorboards) ?

It is my understanding that terminals 2 & 5 are the Line in, and that 3 is the "anti-tinkle" conductor

Q.5) Am I right ?
Q.6) What are / were terminals 1, 4 & 6 for ?