Weather and clothing

The weather there can be a little unpredictable. Sometimes in March it is quite hot while other years it is cold. My advice would be to bring a little of each. It shouldn't stay cold for too long so just bring a few warm items that you can layer if need be. Fleece is warm and light. If you have a down vest it may come in handy. A light weight rain jacket may prove useful. You will be able to buy warm things there as well. You can get warm shawls for less than 200 Rupees.
If you are staying for two months you can rent a room with a kitchen by the month for 4500Rupees a month and up. I would recommend finding a regular room for the first few nights. There are plenty of places listed in the guide books. Om Hotel is very close to where the bus lets you off. It has a resturant and a great view. You can then explore the town and figure out where you want to live. Many of the long term guest houses are not marked as such so you will just have to ask. If you are going there for meditiation I imagine you are looking for somewhere quiet. I would sugest looking for a place along the road/path that Chonor house is on. It is a peaceful area with nice views. Just follow along it and ask at every place. There are also a lot of long term places down the Yongling stairs and up Tipa Road. You will be arriving during the peak tourist season so I am not making any specific sugestions as many places may be full. I have been in dozens of guest houses in McLeod Ganj so I know there are plenty of good ones to choose from.
Have a great trip!