My son behaved very much like this and then some at age 3.  He had obsessios, compulsions and horded every little blue, small, shaped or colored object he could get a hold of.  He had a box by his bed and in the livingroom full of things that "might come in handy."  This took up our days, our lives.  Every doctor we saw just said he had behavior problems and I, I repeat, I needed to change it.  Well after a year and a half of being put down as a parent by most everyone I spoke to or paid to give me their opinion and after the Child find Clinic in my county told me he must be emotionally or mentally disturbed we finally came across a Psychologist that wanted to find out how smart he was and suggested he have educational and psychological testing done.  Her goal was to prove that he did not need special education services.  They found our how smart he was alright and they found out he had a disability.  He has Asperger's Syndrome.  That is when I found out exactly how to help my son.  The recommendation that you make him do things for himself was actually a good one.  Never allow him to drag you or any other family member into his obsessions and compulsions.  The more work my son had to do for himself the less obsessed he became.  I don't excpect this to ever go away completely, but it doesn't have to take up your entire day.  It will be hard and very unpleasant for a while, but things will get better.  My son does not take any medication.  He is in a regular classroom with a great teacher.  He has friends!  A first for him.  He is in Kindergarden.  He is becoming more and more flexable.  His teacher is flexable also so this helps so much.  
Have your child evaulated.  Go to your school system and see if they will do it for you.  If they don't help you please do not stop until you find the help you so need and deserve.
You can talk to me anytime about this.  I WILL NOT pass jugdement and probably have already been there myself anyway.

Barbara Howard  Mom to Samantha 9, ADD and possible Bipolor, Max 6, Asperger's Syndrome and Corbin 4, ADHD with speech disorder and fine motor delay.  (I LIVE IT EVERYDAY)

My daughter, whom just turned four two days ago is also the same way.  (I feel for you, believe me.)  I have three other children that were nothing like her and I know people may think she is the "baby" and that is why she does what she does, but this is not true. She is not handed anything she wants but insists upon everything her way, or as you said, her day is a living hell for all of us. This ranges from me not making the rain stop, to what is coming on television next.  Nothing works....I just hope that interaction with other children at school this upcoming year will help.  Good luck to you....I know I need it.

No, you're not at all unreasonable to be concerned about your son's compulsive behaviors. They are certainly not within the norm for his age, and to the extent that they interfere with accomplishing the normal demands of everyday life they need to be addressed. He shows signs of a likely anxiety disorder, and such conditions have a strong hereditary component. Try to arrange for an evaluation by a mental health clinician who specializes in the diagnosis and treatment of childhood conditions.

I'm afraid that I was not precise enough when describing the issues with my son. Is it perfectly normal to obess about turning the television off and on, then running to the light switch and doing the same, then running and opening and closing all the doors, repeatedly through-out the day?? I have observed that most children at this age do not care less if all the doors are open, or if a light is left on in a room. Even if it is broad daylight, and the sun is shining through the window, my son will NOT enter a room until the light is on. This isn't an "every now and then" thing. It happens constantly. It is his main focus. Even at his birthday party, surrounded by gifts and other childre, he was more interested in the lights and the t.v.
Am I crazy for thinking that this is a little off? Re: the incident with the mashed potatoes, we were on our way to a wedding, and I was trying to keep him clean.. so opted to feed him myself. He does feed himself othewise.

You are correct in thinking you'll need to monitor this, but the behaviors you describe with your son do not indicate an emerging mood disorder. There is no particular age to focus on, although it is fair to say that as the years go on it will become apparent if a mood disorder is present. Volatility and irritability in children, both in and outside the home, can often be indicative of mood disorder.

I did not have room to add that I have been diagnosed with Bi-polar, and I am taking medication to treat this. Conditions of this nature run on my mother's side of the family. At what point do I begin to watch for signs in my son, and even my six year old daughter, who also has mild behavioral issues?

In managing your son's behavior, you are perhaps focusing too much on the explanations. Actions speak louder than words when it comes to behavior. When you set a limit, you don't need to explain it, at least not in many words. For example, it will suffice to say: No going in the street; it's not safe. If he defies your limits, employ time out. Don't engage in lengthy explanations - they will not make a difference. Re: his eating, why are you feeding him? He is three years old and should be feeding himself. If he would like to take portions from particular places on the dish, he can do so. Once you become more adept at setting limits and managing his noncompliance you'll likely be less worried about him.