Yes to all questions.
I respond to every comment (good or bad). I don't take bad comments personally and most of the time we end up having a bit of fun by the end of the conversation. Critiques are welcomed. I'm extremely thankfully when someone takes the time to give a bit of constructive feedback to help improve my series. Good comments are awesome and keep me motivated, and silly comments are gold! I love having fun, and silly comments start the best conversations.
I visit each new subscriber's profile. While I'm there, I lurk a bit and check out their comic series (if they have one), Reading List, bio, and profile wall. Then I give them a "Thank You" post and try to type a special thank you for each reader, if I can. Sometimes I'll offer more comic suggestions based on their likes in their reading list, or comment on something silly in their bio, like "Bacon bits is the fairy dust of the food community." (there's no way I can past up the opportunity to comment on that) 
I don't give critiques unless specifically asked for it. I feel it'd be a bit rude of me, otherwise. However, I comment with jokes and what I like about a page on other comic series, and always try to say something supportive and uplifting to those that need it.