So, is Territory Creation any good? Are skills measured the same way as basic parameters? And does it stack with his existing methods of lowercase territory creation?
Yes, yes, and yes.
Expanding on those answers-
Are skills measured the same way as basic parameters?
They're rated on a scale of E to EX or [STAR] or whatever the biggest/weirdest thing is supposed to be.
E does
not represent "10 times the height of the human cap" in this instance, it represents a very specific basic level of ability with the particular skill. There's a wiki somewhere that goes into detail about the canon explanations and descriptions of each skill and each skill rank as has been provided across the Lore and Mechanics, but I don't remember where it is or what it's called so good luck finding it.
In this case, E Rank basically means that Joe is now
capable of Territory Creation as his initial floor not accounting for the rest of his abilities. Higher Ranks would mean that his initial floor is more competent or is better able to bend or break the "rules" of the basic idea, but we're not at the point where Joe is boosting his Fate Ranks (yet) so we can set that aside for now.
Is Territory Creation any good? ... And does it stack with his existing methods of lowercase territory creation?
I combined these two because the answers involved are linked.
Now I'm not
really a Nasu Lore Nerd, so you'll need to forgive me for getting things wrong, but as far as I remember it
basically works like this.
Magecraft is broadly speaking "Magic as Mortals can do it without exploding/dying/being Heroically Swole". We've seen Joe use it to replicate Tech/Magitech, and we've seen Joe straight up make Magic Items that only work Because Magic.
One of the things that Magecraft can do is create something called a "Bounded Field" which is basically a magical effect anchored to a location rather than an item or cast as a spell. These can basically do all the things Magecraft can normally do, like create a Someone Else's Problem effect, or activate an alarm or trap (like a Fireball), or act as a protective barrier.
Territory Creation, as far as I understand it, is in essence the same concept as a Bounded Field, brought up to
MurderDeathKill Grail Round Robin Heroic Spirit tier ability.
Heroic Spirits as a (heavily bent, subverted, and sometimes flatly broken) rule are better than any Mortal Magecraft. E Rank isn't very powerful
in Heroic Spirit terms. In Magecraft terms, it
should be beyond
any Mortal Mage-Wizard person within the Nasuverse.
How exactly that turns out is an experiment for the Reader and for the deciding of our LordR.
Now, what this actually means in terms of utility?
If I'm understanding this correctly, Joe now has another layer of magical interactions that he can apply to
any location.
That location is filled to the brim with magi/tech infrastructure and those manic (mantric?) booster fields? Joe can slap a Territory effect on top of it to act as- whatever Joe is able to do with Magecraft? He
should be able to fine tune a booster effect relating to whatever purpose he has to that particular area, as seen with his near conceptual Magic Item Creation letting him tap into more esoteric effects, but in the worst case it'll be a layer of defenses that would require
exceptionally wide reaching sensors to detect and respond to, I think.
So in the end, how useful Territory Creation is will depend on how creative Joe can be with his Nasuverse sourced magics (until he's able to convert different Magic types more easily?). It can either be another redundancy in defense or it can further increase the efficiency of whatever Joe finds the time to apply it to.
I would personally expect the Duplicates to near immediately use it to create a Zero Gravity Room both as a test and because that sounds like something fun to play around in.