1) making the wedges- they are very thin so the exact angle of the hole doesn’t matter really. On my MkI the wedges were about 5mm high at the inboard side and came to a point at the outboard end. The wedge should match the angle of the hull so your measurements may be slightly different. You don’t want to raise the rowlock sockets any higher than necessary as you will be sitting on them! I used marine ply and I think solid wood would just split when you put the hole through it.
2) On Oar length, I had 8ft on the MkI which was OK, but for some reason on my World these feel too short now- maybe the thwart is lower and it makes rowing uncomfortable? I am experimenting with longer oars that are about 9’6″.
3) A ‘sleeve’ (I think a ‘collar’ is the proper term?) will protect the oars from chafe, and help to locate the oars in the rowlocks.
4) Through-bolting is better than using screws, and if you have access to allow this I would do it this way without doubt.