Wow C Dog, I applaud your go-get'm approach. Building your first large system and breeding clowns all at the same time. Makes me feel sheepish.
I have a few of comments for you to consider:
- You do not need 1" thick acrylic to build your overflow. Totally overkill and unnecessary. 3/8" thick sheet is more than adequate and will be easy to work with (cut, router, glue).
- A bean animal/herbie style external overflow is a great idea.
- your MRC skimmer seems to be missing the injectors in the picture. You may know this. I recommend you order replacements from MRC if you really want the skimmer to work well. A lot of experimentation is required for these designs to skim well so I wouldnt suggest building them on your own unless you plan to spend a lot of time tweaking it.
- you might consider asking design questions (such as overflow) in one-by-one threads in the DIY forum. People are very helpful and you'll get excellent guidance and a lot of responses.
good luck