Cellar project

[admwest]

Hi everyone, great site. been reading through a few threads now and the time has come to ask for some help with my own little project that I have some questions about

My house is a mid terrace, 1900, brick, 2 up 2 down with dog leg stairs up the middle and a galley kitchen stuck on the back.
Underneath the stairs is a small room that is 1.6x2.5m that I'm hoping to put a toilet/ sink and washing machine in.
At the moment there are some york flags on the floor. As I will be having a suspended floor I am taking these out to use elsewhere. Do I need to seal the floor with visqueen and lay something on top (concrete?), the cheaper the better as it won't be seen.
The cellar isn't strictly undeground but does go 3ft bellow the original DPC.
The suspended floor is going in about 1.5ft below the DPC.
Do I need to have pressure treated timbers and paint the ends in bitumen?
There is a slight bit of damp in there but is quite well ventilated, once I've ripped all the old plaster and stuff out I'm going to hire a large dehumidifier and leave it in there for a few days.

How do I go about plastering over the DPC? I was going to maybe paint the brickwork with some waterprofing and then skim with mortor before plastering. I understand that plastering over the DPC can create a problem because the plaster creates a bridge for the damp.

Is there a minimum ceiling height? I'm hoping to have about 6.5ft

Thanks in advance for any help, I'm sure I'll be back for more help as I progress