Good morning Fltw.
You have entered my World.
Welcome to big horsepower fly fishing.

Your questions, there is enough to write a PHD there !
"A tough question"......don't think so, just thats there a mountain of informatiion suitable for your answer.

I, myself, fish the salt almost every night of the year with a Double, mainly targeting Blues or as we call them Tailor from the ocean rocks for the surf beach.

A 11 foot Double, to me its too short for saltwater applications other than for boat fishing,
because with rod length comes tip speed and with tip speed comes distance cast.

As a newby to Double Handed fishing please no NOT think in single handed rod loads, as the result will be in the end you will be confused like so many others in the past ! Start the Double World all fresh, just like you had found a new kind of fishing casting tool, be it a spin, baitcaster or what ever.

The first confusing part,
" Mfg Recommendations - 400-600 gr. or 7-10 weight lines"

Single handed loads for 7 to 10w are approx, 185+-8grains, 10w+-10grains.

I just viewed the TFO web page and Deer Creek TH Rods for further information that might help you and discovered that the Deer Creek rods were designed as Spey type Doubles and not as Overhead type casting Doubles.

Generally, Spey type loads are heavier than Overhead casting loads, eg
S, 10w, 650 to about 700grains
OH, 10w, 600 to 650'ish grains

They, both types of Double rods have different designed applications.
And as such, myself I would never use a Spey rod for Overhead casting, I would use a OH rod for Spey casting.

You may have noticed that the suggested loads from the manufacture are wide ranging, unlike single handed rods, this is normal with Doubles both S and OH types, this is also called by some as Butt and Tip loads, that the rod is suitable to cast.

Your questions, I will answer them if you like, but for your TFO rod.. ??

Kindest regards,
UB