Hello! I'm glad to hear you are coming to my city next year! And it's not so difficult for me to give you answers to your questions.
1. Best season to visit Moscow is probably summer. In summer, there're so many parks, entertainment, swimming pools, etc. You may take your camera and take photos of the city from mountains and high floors of buildings.
2. Take shorts, dresses, sandals, swimwear, leggings, skirts and tops. It's warm in Moscow in summer, you know.
3. Most convenient transport in Moscow is a taxi, but it's quite expensive so you may count metro as a convenient transport as well. It has got USB charger and soft seats. Hope you'll find that informative and interesting,Regards,(name)