I'm now going through the sefer Kol Hator, from which I recently posted R' Chaim Friedlander's introduction. As I see concepts of interest, I will bl'n try to post them here.
It says as follows, in פרק א אות ב:
According to our teacher, the Gr"a, all that is involved with kibbutz galios (ingathering of exiles), building of Jerusalem, and bringing about more inhabitance of the land of Israel as a prerequisite to the return of the Shechina (Divine Presence); this work itself, as well as all of its details are included in the goal and purpose of the Moshiach that starts the process - the first Moshiach. This is Moshiach ben Yosef, who is the supernatural power that helps every action that is done through an Awakening from below, through natural means, because Moshiach ben Yosef is from the land, and Moshiach ben Dovid is from the spiritual realm, corresponding to the aspect of Rochel and Leah, as is known in the עקבתא דמשיחא (the footsteps of Moshiach) and the קץ המגולה (the revealed end). Moshiach ben Yosef is also further split into two aspects. The first is the aspect of Yosef the son of Rochel, who is of the land, while the second is the aspect of Yosef the son of Yakov, who is of the spiritual realms.
He continues in אות ג:
According to our teacher, the Gr"a, if they have not merited, the beginnings of the redemption will occur through an awakening from below, as it did in the days of Koresh (Cyrus) in the second Temple period, which will come from the left side, which means the attribute of justice. The verse in Shir Hashirim which says "שמאלו תחת לראשי" - His left hand is under my head - refers to Moshiach ben Yosef [and the idea we just mentioned that the redemption begins from the left side, through judgment], and it will be with the permission of the nations. Afterwards, the redemption will come to completion from the right side, which is the attribute of חסד, kindness, and also through the line of רחמים, mercy [which is the center], as the verse says "וברחמים גדולים אקבצך" - and with great mercy will I gather you.
According to our teacher, the Gr"a, the ingathering of exiles that occurs at the first stage of Geulah comes in a manner of captivity, and subsequent redemption from that captivity, as the verse says "ופדויי ה' ישובון ובאו ציון ברינה" - the captives of Hashem will return and come to Tzion with joy. [Note that Tzion is the same gematria as Yosef - ag.] This is all accomplished by Moshiach ben Yosef - the redemption from physical and spiritual enslavement. ישובון - they will return - is plural, implying a dual redemption. This refers to the two returnings: one to Tzion [which is the physical], and one 'returning' of Teshuva [which is the spiritual]. This is the secret of the verse "ששון ושמחה ישיגו" - Joy and gladness will be reached. [The word ששון has the word שש at its root, which can also be read as the number six, with shin's instead of sin's. This is reference to the job of Moshiach ben Yosef, who is the concept of the Tzaddik, who corresponds to the Yesod, which is the sixth aspect of the concept of ז"א. It seems that the ששון is reached through Moshiach ben Yosef, while the שמחה is reached through Moshiach ben Dovid, as is mentioned in the notes here, quoting from elsewhere in the Gr'a's works. Here, however, he is explaining that Moshiach ben Yosef accomplishes both of these aspects - one physical and one spiritual. This would correspond to the statement earlier that Moshiach ben Yosef has two aspects, one of the spiritual realms and one of the physical realms. - ag]
The general concept here, according to our teacher the Gr"a is that all things that are to come about in the completion of the redemption begin at the first stages of redemption "קימעא קימעא" - slowly, slowly, in the 999 steps of Moshiach, the steps of the sheep.