Reducing the size of the cost of the order can be done by editing the CSS for your checkout, which is typically called checkout.css.liquid in your template editor.
As for the bad grammar, I'm not too sure what's going on there, as it should read "Not you? Sign in as a different user". You may want to reach out to our design team about that to see if there's anything they can adjust there for you. You can reach out to them at firstname.lastname@example.org
There's no way to remove the Company and State/Province fields, as there are very few edits you can make to this page.
As for making the phone number required, it's only really possible to make it appear required as per this help doc here:
Talk to you soon!