I have just got a 1968 2 door saloon.

I knew that it needed work on the sills. I have taken off the sill finisher and sill kicker.

I can see the outer sill is gone. The bottom of the Boxing Panel is starting to go. Should I repair or replace this? Is this a hard job?
I also think that the inner sill is going (if that is the part that is the same level as the outer sill and join to the boxing panel).
The cross member end could do with replacing.
Any advice for someone who has never done anything like this before?
Thanks
Iain