Formula 175 for a beginner?

[11onze]

Hi all,
I am a beginner in windsurfing and I am considering buying a set of second-hand gears recently.

Now, there is a deal: someone is selling his Starboard Formula 175 (yr 2000?), Hypersonic 105, Tectonic fin 42cm and Niel Pryde Diablo sail 7.4 m2.

My questions/doubts are:
1) which board is more suitable for light-wind condition?

2) which board is better to go with the NP 7.4 sail?

some background infos:
1) I am around 55kg.
One piece of info I found on line says Formula 135/155/175 are suitable for surfers with weights at 45-60kg, 60-95kg, 85kg & above. (maybe the data are for experience surfers?)
- I would like a board easy to maneuver.

2) The wind isn't strong most of the time in Singapore.
- I want to spend as much of time as possible on the sea every weekend to practice rather than sitting on the beach waiting/praying for the wind to become stronger.

3) the board I rented in a local sea sport club is Mistral Prodigy (255L), which I felt stable at first, then 'clumsy' when I tried to go fast on the water with light waves.
- I would like to have a shift as smooth as possible from the starter board to a new board and go for speed when the time comes. 255L to 105L may be a too big a change for me?

Thanks a lot in advance for your kind suggestions/answers.