what are some things I should've accomplished by now in sophomore year?

You don't need to accomplish at this point in time, but it can give you an advantage compared to others. Some people have done almost nothing by sophomore year, while others are extremely prepared. I would recommend trying to get a leadership role in a club or activity you enjoy, or even better, create a club in your school. Also, activities that have to do with your major or liked subjects are better. Maybe try to join or do something that could get you awards, like debate team, music or sports competitions, etc. In general, focus a lot on a couple of activities that you like and are good at. It's okay to drop one you have now in order to dive deeper into another. Also, having amazing SAT/ACT scores is also very important, so don't do too many things that you are overwhelmed and won't do well in school. I would recommend starting to think of a major or area of study, as some of your activities should be related to that. But, don't worry too much as everyone accomplishes things at different times.

It would help if I knew a little more about how deep those ECs are. For example whether or not you hold any leadership positions. 10 ECs sounds like a lot but it's okay if they are weak for sophomore year. Next year, as a junior, is really the year to stand out as an applicant. Make sure you try to get some leadership experience and if you do any competitions, awards look really good. Right now you should start to think about what you want to do when you grow up and start setting some goals if you haven't done so already. Colleges like ECs related to your major so if you want to go into journalism, for example, maybe you could start writing for the school newspaper. You can start thinking about which colleges you want to go to and making a list. There is no standard answer for this question but at least it sounds like you're trying out a few things which is just fine for sophomore year.

There is no right answer to this question. Accomplishments are personal and there are many to have. I would instead focus on the future, seeing as you cannot change the past. 10 ECs are a lot, but have you put effort into all of them? Next year find the ones you like and invest yourself in projects and leadership positions. A "spike" in your ECs will show colleges more about you. Quality over quantity. Try to find competitions to distinguish yourself in at a state/national level as well. Essay contests, olympiads, debate teams, sports, etc.