Temporary Cellar Renovation

My Victorian terrace has a large cellar that, while not liveable, is pretty dry and doesn't smell.

Long-term, I'd like to convert it into liveable space but we don't need the extra room right now and it'd be expensive to do as it might involve lowering the floors. I'm 6'3" and can stand up in it, but some of the joists are a little close for comfort!

As a temporary solution, I'd like to tidy it up a bit and make it a little less miserable. Here's what I had in mind:

1. Pull down the lath and plaster ceilings
2. Hide the services amongst the joists
3. Install Celotex insulating boards between the joists (optional...it's not really that cold down there in winter)
4. Install plasterboard ceiling with spotlights (optional, I think it'd just look much cleaner)

This would have the effect of making the rest of the house warmer, improving lighting in the cellar and hiding the existing services which are a bit of a mess.

Questions

1. Would the ceiling insulation have to be removed if we converted into liveable space?
2. Are there any issues running the services between the joists if we plan to insulate as well?
3. Is it recommended that a membrane and sump pump are used on all conversions these days?
4. If so, how much space is taken from the walls/floor by the system?
5. Is it possible to excavate anything without underpinning/consulting with neighbours? The brick walls run deeper than the floor but I have no idea how deep they go.

You don't need the extra room right now so why do you need a temporary solution to a problem you don't have. Do it once & do it properly when you need it. I don't think it is a diy job so your builder will be the best person to answer your questions after seeing the site.

OK thanks. I might just put some industrial shelving in there for now then