As a senior engineer, I want to make sure that my time is spent effectively. That being said, how do I evaluate the business impact a project has and prioritize all the different things on my plate accordingly?
On a side note, how do I make sure that the scope of projects are matching my level or exceeding it?
how do I evaluate the business impact a project has and prioritize all the different things on my plate accordingly
In a small startup, this should be quite easy. I used the following filters
how do I make sure that the scope of projects are matching my level
You are in a seed stage startup. You should leverage that. Go to leadership and be upfront. You can directly ask them whether you are driving useful projects for the business.
source: I was an early employee at a small startup
Adding to Seed's great answer, I also wanted to call out that some of this depends on the company size. Since you're at a seed stage startup, it's probably too early/small to have formal levels.
In the early days of a startup, being senior effectively boils down to "people trust my opinion + feedback, and the work I'm doing is critical to the #1 company priority". It's going to be based more on gut feeling and perception rather than a well-defined engineering ladder.
Since you probably don't have a formal engineering ladder, it's interesting how you frame the question around what "exceeding" expectations looks like at your level. I would not worry about that. If you're senior at a startup, your goals and the company's goals to be closely aligned: have you found product market fit or not?.
(If your startup is much bigger, please do correct me!)
That being said, how do I evaluate the business impact a project has...
...prioritize all the different things on my plate accordingly?
On a side note, how do I make sure that the scope of projects are matching my level or exceeding it?
For this, I recommend this Q&A on what a senior engineer project looks like.
And of course, talk to your manager (as always).