Post Sclerotherapy. I recommend that my patients exercise immediately following sclerotherapy to reduce likelihood of deep vein thrombosis, which is rare. Others recommend no exercise, presumably to reduce venodilation, which could theoretically recanalize the veins (?). There is no hard data to support one recommendtion over the other.
Comfortably. My generaly advice is: anything you can do comfortably, is ok to do. If it hurts, don't do it.
As you would like. I advise patients to wear stockings & to do at least 30 minutes of aerobic activity each day for a week after sclerotherapy. Common activities are walking, biking & treadmill, at whatever pace they like. I recommend they avoid heavy weight lifting for a one week period. One practical point- it may not be comfortable to do vigorous aerobic activity since they will be wearing stockings.