How often is it okay to have fried food? Once a week? Twice a month? Once a month?

Some questions 4 U. 1) Fried in what? 2) Volume (one french fry or a basket-ful)? 3) Underlying medical problems (e.g. diabetes, hyperlipidemia, biliary colic...)? You get the point--there is insufficient information to personalize your answer. For the general public, the answer is: "in moderation."
To have Fatty Foods. I commend you for your interest in your Health. You do not need to deprive yourself of a fried food, preferably cooked in olive oil once a week. Take this fatty food as part of Complete meal based on Balanced Diet. For good Well Being: Use Breathing Relaxation, Visual Imagery, Tai Chi, Yoga, Meditation, Music Exercise Be easy on yourself.
No guidelines. This depends mostly on your current health, weight, and family history. Suffice it to say, that fried foods in General tend to raise cholesterol and pack in many calories, which can increase weight easily. Although I am not recommending any particular cut off, they should be enjoyed as infrequently as possible, although they do not need to be avoided altogether. Good luck.