Praise be to Allah.
We ask Allaah to bless your efforts and to increase you in knowledge, guidance and strength.
With regard to the first question, there follow some books which we recommend to you:
1.Nawaaqid al-Eemaan al-Qawliyyah wa’l-Amaliyyah by Dr. ‘Abd al-‘Azeez ‘Abd al-Lateef
2.Nawaaqid al-Eemaan al-I’tiqaadiyyah by Dr Muhammad ibn ‘Abd-Allaah al-Wuhaybi
3.Dawaabit al-Takfeer by Dr ‘Abd-Allaah al-Qarni
4.al-Hukam bi Ghayri ma Anzala Allaah Ahwaaluhu wa Ahkaamuhu by Dr ‘Abd al-Rahmaan al-Mahmood [available in English under the title Man-Made Laws vs. Sharee’ah, published by International Islamic Publishing House, Riyadh, Saudi Arabia].
5.Wujoob Tahkeem Shara’ Allaah by ‘Abd al-‘Azeez ibn Baaz
6.Zaahirat al-Ghuluw wa’l-Takfeer: al-Usool wa’l-Asbaab wa’l-‘Ilaaj by Dr Naasir ‘Abd al-Kareem al-‘Aql
7.al-Ghuluw fi Hayaat al-Muslimeen al-Mu’aasireen by ‘Abd al-Rahmaan ibn Ma’al al-Luwayhiq
With regard to the second issue, there follow some books which we recommend to you:
1.al-Waasitah bayna al-Haqq wa’l-Khalq by Shaykh al-Islam Ibn Taymiyah
2.Qaa’idah Jaleelah fi’l-Tawassul wa’l-Waseelah by Shaykh al-Islam Ibn Taymiyah
3.Ghaayat al-Amaani fi’l-Radd ‘ala al-Nabahaani by al-Aloosi
4.al-Tawassul Anwaa’uhu wa Ahkaamuhu by Shaykh al-Albaani [available in English under the title Tawassul: Seeking a means of nearness to Allaah – Its Types and its Rulings, published by al-Hidaayah Publishing and Distribution, Birmingham, England].
5.al-Radd ‘ala Shubuhaat al-Musta’eeneen bi Ghayr-Allaah by Ahmad ibn Ibraaheem ibn ‘Eesa
6.Fath al-Majeed Sharh Kitaab al-Tawheed by ‘Abd al-Rahmaan ibn Hasan Aal al-Shaykh
7.Tayseer al-‘Azeez al-Hameed Sharh Kitaab al-Tawheed by Sulaymaan ibn ‘Abd-Allaah Aal al-Shaykh
8.al-Irshaad ila Saheeh al-I’tiqaad wa’l-Radd ‘ala Ahl al-Shirk wa’l-Ilhaad by Shaykh Saalih al-Fawzaan
and there are famous books of fatwas by Shaykhs: Muhammad ibn ‘Abd al-Wahhaab, Muhammad ibn Ibraaheem, ‘Abd al-‘Azeez ibn Baaz, Muhammad ibn Saalih al-‘Uthaymeen, as well as Fataawa Shaykh al-Islam Ibn Taymiyah, Fataawa al-Lajnah al-Daa’imah. These books contain a great deal of useful information on the issues mentioned in the question.
And Allaah is the Source of strength.