Zak: Try wearing a different type of underwear to see if that helps with the problem. You might find that it is because your underwear is too tight or too loose, so changing to a different type of underwear (from boxers to briefs or vice versa) can help. Other than that, your clitoris will eventually get used to this stimulation and stop bothering you as much.
Zak: I’m not 100% sure about the answer to this, although I have known trans* men on testosterone who have donated blood in the US. Taking testosterone in-of-itself should not disqualify you from donating blood, provided you are getting your testosterone through a doctor (not taking “street drugs”) and don’t share needles. Being transgender also shouldn’t disqualify you from donating blood, although if you have sex with men who have sex with men you may run into the ban on gay men donating blood and could have some problems. In general though the best thing would probably be to go and try to donate blood and ask the people there what the rules are concerning trans* people on HRT.
Zak: There are a lot of packers on the market to choose from. A lot of people start out packing with the Mr. Limpy small or extra-small (I’d recommend the extra-small if you don’t want a super noticeable bulge) because it is affordable and mostly realistic in size, look, and feel. However most places only sell it in bubble gum pink instead of the usual 3 skin tones (beige, light brown, and dark brown). The Sailor Soft Pack is also very popular, though it is firmer and more expensive than the Mr. Limpy line. The Mr. Right is probably the most detailed packer available on the market that is under $100. It’s made of high quality silicone and is likely to last longer than the Mr. Limpy. There are also high-end packers that can be bought for significantly more money that are incredibly realistic, as well as 3-in-1 packers like the Peecock that can be used for packing, playing (sex), and peeing. Transguys.com has an excellent packer showdown that you can check out for more detailed reviews of a variety of packers.
Adrian: You will need to be on some form of exogenous testosterone for the duration of you “stay” in your masculinized body. There won’t be a point where you’ve crossed some imaginary threshold of no return from a physiologically-masculinzed self. If you want to keep your male secondary sex features, you will have to remain on testosterone.
You’re right though, some changes are not reversible, but many of them are.
Zak: As Adrian said, some changes are reversible and others are not. Some people choose to stay on testosterone their entire lives and others do not. What you decide will have to depend on what changes are important to you and your goal in transitioning.