Update: per comments by the OP, addressing non- (namely pre-) chasidic "books that chassidim themselves use to inform their" etc.
Reishit Chokhmah has not been mentioned. But especially Tikkunei Zohar deserves special emphasis; of all sefarim, with TZ R' Nachman was regularly involved the most, even year-round and not only Elul (Sichot Haran #128). He prescribed to learn all the holy books (Sichot Haran #76, a schedule of learning). In Shivchei HaRan #7 more books are enumerated that he learned:
וְהָיָה מַתְמִיד בְּלִמּוּדוֹ מְאֹד. וְלָמַד הַרְבֵּה מְאֹד שַׁ"ס וּפוֹסְקִים וְתַנַ"ךְ וְעֵין יַעֲקֹב וְסִפְרֵי הַזֹּהַר וְתִקּוּנִים וְכָל כִּתְבֵי הָאֲרִ"י־ז"ל, וּשְׁאָר סְפָרִים הַרְבֵּה מְאֹד וְסִפְרֵי מוּסָר הַרְבֵּה מְאֹד. The Rebbe [Nachman ztz"l] devoted every available moment to his sacred studies. He spent much time studying the Talmud, the Shulchan Arukh,9 the Bible, the Ein Yaakov,10 and the mystical books of the Zohar,11 the Tikkuney Zohar12 and the writings of the holy Ari.13 He also delved into many other sacred works, especially those involving Mussar.14
וְאָמַר: שֶׁכָּל הַסְּפָרִים קְטַנִּים הַמְדַבְּרִים מִמּוּסָר כֻּלָּם הָיוּ בְּבֵית אָבִיו. וְלָמַד מִכֻּלָּם. גַּם לָמַד הַרְבֵּה "רֵאשִׁית חָכְמָה" וְאָמַר בְּפֵרוּשׁ: שֶׁלָּמַד אֶת סֵפֶר "רֵאשִׁית חָכְמָה" פְּעָמִים אֵין מִסְפָּר. The Rebbe said that his father’s library contained all the small Mussar books and that he went through every one. He also spent much time with the Reishit Chokhmah,15 stating that he reread this remarkable work countless times.
וְגֹדֶל בְּקִיאוּתוֹ בְּכָל הַסְּפָרִים כְּפִי מַה שֶּׁרָאִינוּ בְּעֵינֵינוּ קְצָת הָיָה בְּלִי שִׁעוּר וּבִפְרָט בְּסִפְרֵי תַּנַ"ךְ וְ"עֵין יַעֲקֹב" וְכָל כִּתְבֵי הָאֲרִ"י וְסִפְרֵי הַזֹּהַר וְתִקּוּנִים, לֹא נִמְצָא דֻּגְמָתוֹ בָּעוֹלָם. The Rebbe’s unique expertise in all sacred literature was obvious. He was particularly unique in his knowledge of the Bible, the Ein Yaakov, the Ari’s writings, and the Zohar and Tikkuney Zohar, to the point that literally no one could be compared to him.
כִּי כָּל הַתּוֹרָה כֻּלָּה הָיְתָה מוּכֶנֶת לְפָנָיו וְשָׁגוּר בְּפִיו כַּשֻּׁלְחָן הֶעָרוּךְ מַמָּשׁ, כְּדָבָר הַמֻּנָּח לִפְנֵי הָאָדָם לִפְנֵי עֵינָיו שֶׁיָּכוֹל לִקַּח לְעַצְמוֹ מַה שֶּׁיִּרְצֶה, כֵּן מַמָּשׁ הָיוּ כָּל הַסְּפָרִים הַקְּדוֹשִׁים מוּכָנִים לִפְנֵי עֵינֵי שִׂכְלוֹ הַקָּדוֹשׁ בְּכָל־עֵת שֶׁרָצָה. וּקְצָת מִזֶּה יְכוֹלִים לִרְאוֹת וּלְהָבִין בִּסְפָרָיו הַקְּדוֹשִׁים. He was fluent in the entire Torah. He could quote anything in the sacred literature as if the book were opened in front of him. It was like a table set before him, where he could see everything and choose what he desired. The entire scope of our sacred literature was like this, standing ready before his mind’s eye to be used whenever he desired. This can be seen to some extent in the Rebbe’s writings.
Also it should be noted regarding the term and concept "philosophy" - חקירה - (philosophy; rationalism; questioning or undermining the tenets of faith) - it is something direly warned against in particular in Breslev. "Derekh" or "way" might be better term in your question.
צָרִיךְ לְחַזֵּק אֶת עַצְמוֹ בֶּאֱמוּנָה וְלִבְלִי לִכְנֹס בַּחֲקִירוֹת כְּלָל, וְלִבְלִי לְעַיֵּן כְּלָל בִּסְפָרִים שֶׁל מְחַקְּרִים, רַק לְהַאֲמִין בְּהַשֵּׁם יִתְבָּרַךְ בֶּאֱמוּנָה לְבַד בְּלִי שׁוּם חֲקִירוֹת כְּלָל. Strengthen yourself in faith, completely avoiding all speculation. Do not look into philosophy, but believe in God with innocent faith.
... (see there)
And there's an entire section in Chayey Moharan against Chakira:
About the philosophical books he told us a great deal, many times. And he utterly, utterly forbade us to even look at them at all, God forbid. He put extraordinary stress on the severity of this prohibition, because they very much confuse one's religious views with alien views that do not at all agree at all with the views of our Holy Torah. They [the authors of these philosophical books] also do not believe in demons whereas all the words of the Talmudic Sages say the opposite. Especially now that we've been privileged to [the revelation of] the Zohar, the books of the Arizal and the Baal Shem Tov of blessed memory and so forth, which are all founded on Ruach Hakodesh and greatly inspire a person in truly serving His Blessedness.
... (see there)