I guess I'll give it a try anyway.
1. I will come back often (to hang out)
자주 = often, 놀다 = play/hang out, ~러 = in order to, 오다 = come, ~ㄹ게 (mispronounced as 께) = future tense in response to someone
2. This might be a basic expression I am not aware of, but I am going to break it down at least. Also Naver and Google Translate give different answers.
잘 = well/good, 보다 = see/look, ~고 = and, 가다 = go
Edit: I asked my Korean friend, and it is common expression when you're leaving (a store for example). "I had a good look, and now I go"
요 = polite ending
~ = being friendly. The more the friendlier
As for the reply bit, perhaps 정말요? 감사합니다~~~
Really? Thank you~~~