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.