Weight varies from person to person and change over time, as increased muscle mass and strength. Do not worry that your muscles will increase so much that it becomes unsightly is not the case.
Circuits can be done virtually anywhere, it is important to be enough room. It is good to observe time, even if at first you'll find it difficult, because the only way you will get the required intensity.
If this is the first time you do sports or been a long time since the last anternament indicated is to perform a medical examination beforehand.