Damp soil under floorboards of Victorian Terrace

Hello! I am very excited to have recently become a homeowner AND to have found this website! I've started my renovation and am knee deep in trying to solve some damp problems stemming from a leak in the roof. Pete Ward's book, The warm dry home has been a great resource. After lifting some floorboards to see what's going on under there I have been trying to work out what to do next. I've stalked all previous posts regarding soil under Victorian homes and the importance of ventilation. I only have one air bick at the front and one at the back Before I cover all of the floors with new flooring I'd like to make sure everything is set up right below.

First pic is taken in my front room - the soil is pretty dry and there is quite a gap between the joists and the soil. The joists are rotten at the end touching the wall. Second pic is a close up.

Ideas so far: Cut off the rotten ends of the joists. Screw or bolt new timber the the good bit. At the wall remove the rotten parallel support timber by the wall perhaps replace with slate. Put some DPC around the end of the new timber joists.

Third pic is in the dining room on the ground floor on the side of the roof leak. The wall is damp and needs to go back to brick. The soil is pretty raised and very damp in places - I'm not sure if this is from the roof leak or otherwise I've checked inside the foam insulation of the water pipe running through and it doesn't seem to be wet. The timber running parallel to the wall supporting the joists isn't dry.

Ideas so far: Make sure there is 100% no leak from water pipe. Dig some soil out to leave a bigger gap between floorboards. Maybe try and get some slate under the joists and also wrap in DPC?

I'm convinced that this must be a job I can do myself, so any intel would be very welcomed and very very much appreciated! X

Check outside drain gully. Rain water can get through cracks in drain capture and get under the house.
Make sure all the water in all the drains goes down and away as it should

Check beyond the gully, a bust pipe near the house will make great use of the house as a soakaway.

I'd suggest your neighbour had the right idea - concrete, as it's pretty shallow so it won't cost a huge amount. You'll end up with a much better insulated floor so will have lower heating bills and greater comfort for ever. Plus you won't have to worry about groundwater, vents and mice ever again.

Peter Ward is something of a one-man religious cult. Some things are good logical sense, but he also has some stupid theories that are based on his own hunches, are not backed by any science and are the opposite of what everyone else says. His advice would be good if you lived 100 years ago and didn't care about being cold.