How many kilos is it ok to lift at the gym considering l have a L5-S1 ~5mm hernia? I haven't had any sciatica problem from it. I'm 5'2" and 110 lbs.

See a physiatrist. It is wise of you to investigate these limitations. However, this isn't something that can be answered generally, and requires an understanding of your body habitus, history of training, planned activities, etc. A Physical Medicine and Rehabilitation specialist can assist you in assessing your overall limitations by both evaluating your various tests and your physical examination.