(Work in progress)
This site is a fantastic resource, with detailed articles about a variety of commonly discussed topics including comparable dosages between various forms of estradiol, proper dosages of cyproterone acetate, sublingual use of estradiol pills, and the influence of estradiol on blood clot risk. Their intro to transfem HRT article, and interactive injectable estradiol levels simulator are particularly useful. Also quite interesting is their exploration of HRT options for people with nontraditional transition goals, such as transfem nonbinary people who desire demasculinization without breast growth.
In my opinion the best successor to the now sadly defunct hrt.cafe, this site is a fairly comprehensive list of non-prescription suppliers who are known in the community, and is an easy way to compare prices/sellers.
r/TransDIY is one of the largest and most active DIY HRT communities, and is an incredible resource. Though many trans subreddits have a reputation for dogmatism, brainworms, etc., this is one of the more tolerable ones in my experience.