Rubella IgG antibody is +ve; will it be any problem to conceive?

No. Rubella, or any, igg antibody, is your body's response to exposure to an infection, such as a bacteria or virus (antigen). A positive result means you have immunity and do not need a booster.
No effect at all. This study has no effect on your ability to conceive at all. What it does tell us is that if you do get pregnant, neither you or the fetus would be at risk for rubella during pregnancy. (Which would be bad)