How do you do it?
I cook, I refrigerate, I freeze. Depending on how much I cook and when I plan to eat it I will do both. If I plan to cook food for an entire week I will store food for the next ~3 days in the fridge and the rest in the freezer.
How long can the food you cook be frozen/refrigerated?
Depends on the food. Most foods you will cook will be OK for over a month when frozen. In the fridge they will generally last up to 5-7 days.
How do you reheat it? (defrost + microwave/oven?)
Mostly zap in microwave. May defrost a bit on the bench first.
How does it taste compared to making it fresh?
It's always better fresh. Some foods freeze and reheat better than others. Generally reheated from fridge will taste better than from the freezer but some foods are more noticeable than others.
What can't/shouldn't be frozen & reheated?
In terms of food safety most things are fair game. Some foods will taste better than others. Steaks don't go well as they get dry and crappy. Avoid cooked fish, particularly fillets. Nasty smell when reheated. Anything with a high water content will become soggy after freezing and reheating. e.g. don't freeze a salad.
Is it okay to cook chicken, freeze it, then defrost/reheat it later?
Chicken is fine to freeze and reheat. Anything with diced chicken will generally turn out better than larger fillets.
I was thinking of doing a couple chicken breasts and tuna tomorrow with the combination of pasta, rice, potato or veggies & some random sauces. Will it be ok to freeze these & reheat later in the week? Or better to just refrigerate them?
Yes it would be OK - well it depends on what form the tuna is in. With those options personally I would do something like ... chicken stir fry with sauce and veggies (to be frozen or refrigerated). Rice or pasta cooked and can be stored with with the stirfry or separately. I only eat tinned tuna so I would keep the tuna in the tin until I am ready to eat it. It's easy to keep a few tins around ready to crack open and add to another meal when ready.