They probably would only join in if they think they could tip the balance; they wouldn't join in if they thought they'd lose.
Hell no. The British government never really cared about Belgian neutrality, they used it as casus belli. All it would ensure is British neutrality officially (not unofficially) if the French kept their move in the Ardennes.
This book explains the reasons Britain really got into the war, they didn't care about Russia or France since they didn't consider them a threat and probably thought they could work with a reduced power Germany against the French and Russians...much like they did in the 1930s.
Sure, but there is the manpower problem and Habsburg manpower was limited in the face of a civil war and a Russia+little Entente+French potential entry.
Shorter front line isn't necessarily a defensible one when faced with all of the above.
Who said anything about USW? The French could follow cruiser rules. Plus again the whole issue with USW was the loss of US ships, not anyone else's, which likely won't be an issue here.
No, I meant Russia. Russian defeat would probably trigger French entry. I was talking about the CPs actually starting to win and getting jumped on as a result.
Was their excuse for war in 1914 IOTL convincing? As long as the right people don't care you can gin up anything in the age before the internet.