It sounds like you may not be aware of OmniFocus' smart matching of projects and contexts and intelligent date parsing. The only item which can't be done from the keyboard is setting the flag.
When you enter a project or context field, type a few letters and you'll get a list of everything that matches that sequence of letters, without any need for the letters to be contiguous. The first letter of the words in a multi-word project name is often a good starting point. I've got 661 active projects in my database, so I'm not interested in a scrolling list via mouse, trackpad or touchscreen! The smart matching works very well, and I rarely have to enter more than 4 or 5 characters to get the item I want.
The date fields on the Mac do not require you to use the date picker widget. You can type things like "+3d" (3 days from today) or "wed" (Wednesday) or "thu 2w 4:30p" (2 weeks from next Thursday at 4:30pm).