1) Generally you should moor on the towpath side unless there is signage to say you can moor on the offside. You also need to observe that sometimes there is private mooring on the towpath.
2) I have tied to a tree once but it's not the done thing and can cause damage to the tree.
3) Mooring with weights on the canal? You need to make sure your boat is secure to the side of the canal so it does not interfere with passing boats. Use mooring stakes, mooring hooks or goat chains where there is metal pilings. Visitor moorings tend to have rings.
If you can get your boat in sufficiently to get on and off the boat, then great. It's trial and error in many out of the way parts of the canal system. Sometimes the edges are too silted up to moor and the bank unstable.