Conservatives support military reform, and passing a reform gives conservatives in the upper house, so its best to save all your RPs up and pass lots of military techs in one year. As Japan, I passed one economic reform to stabilize my economy, then saved up my RPs until January 1962 - just after the upper house election. Then I passed 7 military reforms, one after another, and westernised in July, 1962.
I wasn't sphered by anyone, but I got a bunch of techs anyway. I researched Iron Steamers and built a few ironclads, then beat up China and in two wars took Korea, Port Arthur and Taiwan. I also took Sakhalin from the Russians and colonized the Pacific.
I then spent 40 years beating up China. I made a bunch of colonies into states (none in Korea or China, alas) and was tech leader by 1900. I just stopped in 1917 - I'm rank two GP and have China down to 4 states, so I can annex it with my next war. The war in China has been a bit boring though - its annoying that it costs 11 infamy to take a region from a substate. I wish there was a way to break these substates off from China, or else they should have a 5 infamy cost, the same as taking regular concessions. I wanted to take Manchuria as this is historical, but ended up having to take a big slice of the east coast instead.
Anyway, Japan is a very easy country to westernise as so long as you can deal with Russia. I agree with some others in this thread that national focuses don't do enough though - it takes a very long time to get clergy, and I think westernising as any other nation would be very tedious (perhaps Hawaii would be ok).
One change I would make would be to the effect of taking the 'imported arms' and 'foreign built ships' military reforms. Imported Arms gives your flintlock muskets at the moment - I would make this improve with time, so that it gives you the tech in this line equivalent to what your sphere master has, or to the worst of the great powers if you aren't in a sphere. The Foreign Ships reform should give you access to tech along the 'Clippers/Steamers' line.