Just out of curiosity, what would be the best use for these? Any recommendations on where they should go, and after what has been done beforehand?

i would say either on a storage warehouse or an arti planet.

heres my plan:

I have a very large arti desert :
I got lucky and nabbed a QSE off of a TO carrier
said desert had a cloak screen when I invaded

bump up passiv cloak ashigh as possible
use talith ability to make x15
use cristals to make x20 ( need 3 more )
use the remaining 5 anchors i have on it
ergosphere extractor
Cross Signal repeater
Meta Tuned Jammor
use QSE to make massive
crystalize for very massive x22

passive cloak of 3500
stealth screen : cloak +30%
Ergosphere Extractor : cloak 150 +20%
Cross Signal Restrainer : Cloak 30%
Meta Tuned Jammor : cloak 25%
dimensional anchor x5 : 450

total : 4600
+ % boosts : 11661
+ 120% legion boost : 27986

all without any cloak structures

passive cloak is a little higher then that heres a link to the highest max repeatable passives
viewtopic.php?t=27372
You can use the Xecti Ensconcing Field to boost cloaking pasted its max(i think) i am not sure if anchors have a cap
i was thinking of getting max passive cloak repeatable 3892 then add Fields to boost past max (if i can) then use anchors to get even higher passive cloak so i won't have to use as many special artis to cloak it completely.
3892 + 180(15)+ 90(15)= 7942 if my math is right before any special artifacts

I'd say on some huge, resource-rich planet that you plan to permanently cloak.