This doctrine, "God is everything" did not originate with the Besht. It is true that the verse of the Torah ["You were shown to know that The Lord is God, there are no gods besides Him."] is explained to support this belief. But the practice and goal of union with the God that created all and permeates all and is All appears in the Upanishads [the final sections of the four Vedas written 1000-500 B.C.E.]
  The first one to make Yoga into a coherent unified system was Patanjali [circa 200 B.C.E. during the time of the Second Temple].
  "Yoga" means "union", i.e. union of the finite transitory self with the infinite "Atman" or "Brahman" [eternal infinite self].
In Yoga-Vedanta philosophy there is one true God that is invisible, imminent, transcendent that created everything. The name the Hindus give to this God is Brahman.
All creation is composed of the substance of Brahman.

  This is not traditional Torah. In the theology of the First authorities (Rishonim - Medieval sages), God is everywhere but separate. The world and God are not one. The world is not made of Divine Substance. It is made from nothing. In Torah thought God has no substance at all. So things are not made from his substance.
Creation ex-nihlo is the view and philosophy and emphasis of the Torah as explained by the Rambam and other Rishonim [authorities of Torah of the Middle Ages]. This is very, very different than the views of Breslov Hasidut or any other Hasidut one that I am aware of.
Modern day Breslov is an attempt to beat Hindu Yoga-Vedanta at their own game. It is not Torah.

Changing the essence and meaning of Torah as defined by the Rambam and the Geonim bothers me.

The "contraction" is described in detail by the Ari. At first, the light of God was everywhere. So there was no place for creation. So he contracted his light and made an empty space like a sphere. [There was also a point of light left in the center of the space.] He then sent His light down through one opening and the light went down a bit and then started curving around and became the first sub sphere (called Keter) in the larger sphere. This happened ten times. This does not imply things are Godliness. 
 The question is not the tzimtzum but the light. And the light is "created light" as stated by the Sefer Yetzira and brought down by the  Ari.

) In panenthism God also transcends the World, and so is not equal to the world. Rather he contains it.
See for example: Lekutim Yekarim from Pinchas of Koretz Parshat Veetchanan: "There is nothing in the world but the Holy One Blessed be He." (This is a later book. It is not from the original books of R. Pinchas.)
Ben Porat [page 126] from R. Yaakov Yoseph brings one story from the Besht that he said "There is no place empty of God." Later the same story in Heichal Bracha (from  of Kamarna) got expanded into him saying, "There is no existence besides him."

) The Ari said [from the Zohar] that the sepherot of Azilut (Emanation) are Godliness. After that i.e. the sepherot of creation, formation, and the physical universe are not Godliness. (Eitz Chayim Heichal 1, Shar 3, chapter 3). [The Zohar says in Emanation alone, the vessels and light are Godliness. After Emanation just the light is Godliness not the vessels.]
This is independent of the "Contraction" question. But concerning the contraction the Arizal wrote, "He contracted Himself." (Eitz Chayim 1:2:2; 1:2:3; 1:2:4) [Not "his light".]

Books of the cult under the excommunication of the Gra  defend the doctrine of panentheism, by going to the zimzum. But in fact it does not help much. Even if it was not complete, things still don't have to be Godliness.]

The appeal of cult under the excommunication of the Gra is entertainment,  emotional value, not truth value. 

The Nefesh Hachaim does say that realizing there are no powers in the world besides God is important. That is not the same as pantheism. That means the world is under the control of God alone.

Nature certainly becomes the stage of God's expression of his will. He expresses his will and purpose through forces of nature in the Torah. But nature isn't God himself. He's not identified with it. He's wholly other. He isn't kin to humans in any way either. So there is no blurring, no soft boundary between humans and the divine, Thus worship of  a tzadik is contrary to Torah.