أحسن الله إليكم Sheikh, when we start reciting a surah but we don't start reciting at the beginning of the surah, is it allowed to say the basmalah before it?

If you are not reciting from the beginning of the Surah, you only say, "A'udhu billahi minash-shaytanir-rajim." This is because "Bismillah-ir-Rahman-ir-Rahim" is an ayah that you recite to separate between two surahs.