Talimul Haq is a good affordable book. I still use it! The content of the link is approved by scholars from As Suffa institute (www.as-suffa.org) Mufti Sajjad & Imam Abadasmad Clark of Norwich. I have mentored reverts and often well intended brother says things that is unwarranted or suitable. Key thing is to make this simple and short. As for TJ, you will gain some practical experience. It is not about joining them but to improve ones understanding in practical terms with meaning. In absense of any other practical avenue, this is a good way to start things off! i found it beneficial when I started to look into deen. I have read many books before but needed some practical example and how one can understand tawhid and risalat and internalise it.