ask expert here about hepatitis B vaccine?

I checked at summer 2009 in china, have Hepatitis B surface antibody positive, and all others (4-checkups) are negative. This indicates me having the antibody by hepatitis B vaccine. I don't have any recent blood checkups.

Since I am going to china quite often because of work, I was just wondering whehter I should take  Hepatitis B vaccine again as a booster without checking my blood again? Will it harm my liver because of this extra shot?

Also could I take Hepatitis A vaccine at the same time with Hepatitis B if I decide to take another shot B?

Thank you very much for your professional inputs!