1. Just be you with everybody. When others show up, just go around and introduce them to everyone you just met to make them feel welcome and to help engrain their names into your noggin (sucks to be the last one!). Then just say a little about yourself and then ask what brought them to the meetup.
2. I've never had any problems getting newcomers to get engaged in the convo. Most of us work regular jobs and have friends and family who never want to talk about bitcoin, so we're all just sponges for other perspectives and experiences. Sometimes it's hard to get people to talk about one specific thing though. Don't have any advice there except sending out an agenda before hand, but I'd just keep it very short.
3. We struggle with this. Our plan is to start having separate technical meetups because when we all get together after work, people just want to have fun eating and drinking. But we haven't gotten very far there yet.
4. Let things flow at first. Probably important to gauge the experience levels of everyone there so you can select interesting topics in subsequent meetings.
5. Keep background questions to a minimum to avoid giving off a scammer or fed vibe. Don't wear anything with a bitcoin logo; bitcoin adjacent stuff is going to help ppl find you though.

Regarding the tab and paying in bitcoin, you or some other volunteer should offer to pay the whole tab in fiat (use something like fold or gemini card to get sats back) and use something like this app my friend made. You can scan the tab with your camera and then split the items for each attendee who wants to repay you in sats. It handles the tip as well. Very slick when the OCR works (~90%). Requires an LN address though. They get experience paying on LN and privacy from the fiat panopticon, you get their sats, and the network gets stronger.