Hey bubba, welcome to the board! That's one fine thick beard you've grown there, sir! If you've the freedom to just let it grow for the summer then do so. If you get frustrated with the neckline you can always trim that up a bit to make it neater but it's not critical. You have very good natural lines as it is.

Not trimming for the summer should include your mustache, IMHO. All the frustrations you express will only come back as it grows back after each trim, so I suggest that, as the other guys have said too, you just let it grow over the summer. Yeah, you're going to have to deal with hair in the mouth for a while, and I won't gloss over the fact that it can be profoundly annoying, but in the end that will, for the most part, go away. Additionally, your mustache will be fuller and will balance your beard better. Just hang in there and follow the great advice you've received.

Be sure to post your progress here regularly for feedback and encouragement. By the end of summer you'll be sporting an even finer beard than you have now!

Cheers!
Tom


Some helpful links:
Library Central of Beard Growing


Taming the Wild Mustache
Tips for eating and drinking with a big mustache

Excess on occasion is exhilarating. It prevents moderation from acquiring the deadening effect of a habit. ~ W. Somerset Maugham
A jerk with a beard is just a bearded jerk, but a bearded gentleman is awesomeness personified. ~ Triibeard