Yes, you are the wired one! That's not always a bad thing, though.
You can see how itsme might have wondered, however. A word of advice if you don't mind. Your instruments are very interesting! I love to see people building with a different take on things. When designing an instrument, however, don't leave the strings to the end. They should actually be almost the first thing you consider.
Start with body volume - then go to a good range of notes for the body - then to strings that will respond well at those pitches - then to a scale to accomodate those strings.
If you've built and braced your soundboard for light tensions then I don't think the standard Mandocello tuning is the answer. Plain strings will be too thick for any sort of decent sound. It's why steel strings are traditional.
Look at higher pitches if you want plain strings. I'd take a look at standard Mandolin tuning. But rather than say that's the answer, I'll give you a key in how to figure it.
One handy tool (there are others) is StringCalc. It will let you input various materials. There may be sources for flourocarbon in that length, but it also lets you input Nylgut. I know you can get your lengths there.
Here's a link for StringCalc:
http://www.wadsworth-lutes.co.uk/software.htm
and Curtis Daly at Aquila USA has the lengths you'll need:
http://aquilausa.com/ng_strings.html
You can try some of those heavy gauges if you still want your Mandocello tuning, but they'll be pretty bulky and pretty dead.
Best of luck!