1. No microphone isn't required, can use one on your stream if you DJ though if you want to.
2. yeah you can /me which will turn your writing purple like /me says hi would appear like RaspberryKisses says hi
3. That's personal choice, you are limited to a certain amount of letters per post (can't remember the number) so you can emote, not emote, paragraph or not as long as it fits in the limit....or just write multiple messages. Would all depend on what you and/or your partner prefer.
4. 3DX is smaller compared to some so you can go to the public rooms, some are busier than others like Sin Club, Love Island, Beach and then there are the user rooms which will show how many people are in them. You'll get cold (random) invites i'm sure. Sometimes you can find noone talkative, other times you'll find people that never shut up but for the most part people here are nice, friendly and will welcome you. There are trolls for sure but they're easy enough to ignore
If you decide to join, hope you have fun and enjoy the place. It's worth a one month try at least.