Re: handshakes - just don't. Unless someone's been on another planet the last couple of weeks, they'll probably appreciate you not shaking their hand just as much as you appreciate not shaking theirs. So many just automatically extend their hand in a business environment - no one should be doing that now. But they will because it's habit. Use something else; my favorite is a small namaste bow.
Re: large-group gatherings of 250 or more being banned - that's things like concerts, worship services, sporting events, etc. where people are sitting close together. It's not people shopping or working in an environment like we have. (Although in the hand soap section of that aisle, it has been getting a little crowded lately!)
Re: the inevitability of catching COVID-19 - maybe. But unless you're high-risk, it's very likely that it won't be a serious illness for you. Practicing good hand hygiene and social distancing will limit your exposure; other good health habits like staying hydrated and getting enough sleep will help your immune system stay strong so if you are exposed, you'll be well equipped to fight it off. If you do get sick, monitor your progress closely because it CAN - doesn't always! - get bad very quickly and you don't want to wait to get medical attention in that case. But keep in mind that even in countries that have been hard hit, not everyone gets it. So let's stay positive and not assume the worst.