Hi there Mika~!
You mention having grooming figured out which is good, that is certainly one of the hardest aspects to get started with(I was definitely not the intended customer for Manscaped but I will forever be grateful for the help in discovering foil-razors and to help establish confidence I did not have with shaving in the past).
With regards to undergarments--This will vary by person, but personally? Bamboo Cool of whatever style you like(I just stick to bog standard, but they also have "boyshort," style and otherwise) will serve you well. I have no stake in Bamboo Cool, I just genuinely love them and wear them everytime I go off to yonder workplace.
With communities, I would like to give a word of caution: There are a dime a dozen places that may seem good, but you need to watch yourself all the same. And even in the best of them, creeps like to..well, creep. I would personally avoid Discord, but Stoat(outside of its main server) has some good places if you are looking for RTC.
If you have a specific question about anything, I very well might have had experience to share with you. Not Trans myself but I fall under the Nonbinary umbrella as a Femcoded Maverique, and have been through the gauntlet mentally, physically and spiritually. If you have ever heard the song Propaganda by Crusher-P, that will give you a decent primer on my life.
Ask away if you wish, and you are doing fantastic! You are awesome!