Sikkim Travel Help

I’m travelling from Darjeeling to Sikkim next week. Wanted to know a couple of things.

1. How is the road from Darjeeling to Sikkim? Does it have a lot of bumps or is it a smooth ride?

2. Apart from staying in Gangtok, I just have two more extra days. What place should I go, something that is not very far, has good roads.

3. Best place to stay in Gangtok

4. Any suggestion that you wanna give.