For travelling to London, you will defo get a seat on boarding train from Orp but have to be lucky if boarding at Petts wood.
In Orp, be ready to shell out in excess of 0.5 million for a decent 4 bed detached house. Petts Wood is nicer than Orpington but it is hard to get something nice and at the same time "affordable"
. South of Orp is Sevenoaks and Tonbridge nicer but dearer. You may explore Swanley/Dartford/Bexley (8-10 miles) on Rightmove.
I don't like Walnuts. There are no decent shops out there. The high street is full of alright restaurant but tons of other shops you may not like to visit (Poundland, Charity shops and cash for gold type). The better options for shopping are Bromley/Nugent Park/Bluewater.