瑞士 + 意大利 旅遊

Your trip will be 14 days in total, so after deducting flying time, it should be only a 12-day trip. From your planning, I suggest you need to spend at least 7 days in Italy, so you can spend 5 days in Switzerland.
Also, I suggest you can consider flying with Swiss Air. Flying from Hong Kong to Zurich first, then change flight to Rome immediately. Then going back to Switzerland by train. So, the iternary will become as below:

Hong Kong -- Zurich (transit only) -- Rome + Vatican City (3 days) -- Florence + Pisa (1.5 days) -- Venice (1.5 days) -- Milan (1 days) -- Luzern + Snow Mountain (2.5 days) -- Geneve (1.5 days) -- Zurich (1 day)
Bewteen cities, you can travel on train. Train service in Italy and Switzerland is very reliable and comfortable. In case of need, you can also buy a railpass.
For the travel agency in Hong Kong, please avoid finding the one offering you an amazing price !!! It is usually a trick to catch you into their trap. Normally, the difference of ticket price among different agency should be only within 100 - 200, or even less than this amount.
Please quote the airticket on the airline website first, sometimes they may have discount price. Then, comparing the price with the offers from famous agencies. I am not saying small agencies are not good, but if you are not familiar with them, or the agency is not introduced by your friends, then spending 1 - 200 more to get an "insurance" is not a bad idea.