西南歐自助遊一問

If you're not very interested in fashion, I suggest you to cut milan from your plan. It's a boring city, just with a Cathedral. Rome 2days and paris 3 days seem not enough to go to all the famous spots. Rome including Vertican as well...so at least 3 days, and Paris gets lots of good museums (if you like art)...or even you dont' like art, it is worth seeing those real famous paintings.
If I were you, i would go to less city but stay longer...otherwise you will feel very tired and can't enjoy the trip...
I'm not sure what you mean by 儘量保持低消費...for me, I went there for 50days, and spent around $30000. But I ate plain bread most of the time, and just had one good meal in one city...but it's the harsh experience made the trip more memorable :)
I think railpass is the best choice for travel in Europe, and save lots of time...considering you have spent so much money and time to go to Europe, why bother to spend your valuable time on transport, right?