Foundations 50 yr old house on sloping block

Hi,

I am also renovating under my house which is approx 50 yrs old weatherboard supported by single leaf brick with engaged piers. I have a number of issues with it I need solving:
1) Foundations, I am unsure of the existing foundations supporting the bricks due to no drawings etc. The front of the house is supported by single piers and the rear of the house is supported by brickwork. I have a height of 2.7m to the floor level above and I understand I will have some issues with making these into a habitable room. I know there is no draining against the brickwork and I do get some water I suspect from either under the so called slab ( bricks with a skim a concrete over it) or through the brickwork itself ( very minimal) I have been flooded a couple of times but since pluged a hole in the concrete with silastic and it has done wonders (yet to be fully tested). What I can guarentee is the house above has not had one crack in the fibrous plaster or cornice over the time it has been built.
2) I am contenplating on ripping up the concrete and putting agpipe in to provide some drainage and also putting new sewer connections in, is there anything else I should consider?
3) I also have a vision to brick up the whole house down the track since the existing foundation is protruding a good 100-120mm out allowing me to have a cavity between the brickwork, however this means I need to do some serious homework on how to tie all the foundations together (if possible).
4) I am starting to think that I should just knock it down and start again, but the framework is all hardwood and given the time it has currently lasted I think I would be stupid to do so.
5) I also have another post around my extension of the roof but as you can see I need to get my foundations right before I do the roof, or make adjustments to allow the roof to go on and block in later.