It is very easy to walk around the centre of Amsterdam, and everywhere of a touristic nature is relatively close compared to most cities in europe, so no need for trams - hubby pushes me in my wheelchair all over, without problems (including in the -11 temperatures we had last week).
As to the weather, well no one knows if it will rain, but in general, it will be warmer than last week. I had a lovely spring like visit in Feb last year and terrible wind and pouring rain in August, so just get on with it; If you need to buy a jumper and a brolle when you get there, do so and enjoy your trip.
As regards to distance - do you know that google maps have a direction function - this gives you an approx walking time and the directions to do so, and according to this:
1 - VG - Leidensplein = 11 mins and is 850m
2 - Leidenspein - Flower market = 8 mins and is 550m
3 - Flower Market - Dam Sq = 12 mins and 900m
all of above are based on walking at normal walking speed, so ambling and perusing your surroundings will add more time, but distances obviously remain the same.
Have a good trip