You can do one course at a time in a regular mode. The other option  is one course as regular and the course in distance mode.

The decision to choose the field has to be yours.

The scope in both is good but they are different fields. Incase you do LLB after Bcom, it will be a 3 year course. After working in some law firm you will be able to open your own firm and help others in their fight for justice. You can also start your specialization in Taxation and later can also become a tax consulant.

Incase you do MBA after Bcom, it will be a 2 year course. The degree in management program will be highly useful after Bcom. You can open up your own venture and even after an MBA degree you can get eligible for various business, marketing , human resource and sales executive jobs profiles. There are various specializations under MBA you can choose to do as per your interest.

Good Luck.