The community I live in is so ordinary, but I think it ishould be a good community in our city.

"It should be" can be used to describe possibilities, but generally its use is restricted to situations where the situation involved is only hypothetical.

The main reason is that it has a low rate of capacpopulation density.

It is not a businesscorporate housing, but it was built by all of the company’s staff.

You could also write "it is not a business district," but the meaning would be slightly different.

EvWhen if there is a little wind, you will feel it is very heavythe wind is light, you will feel a strong breeze and you can often hear the whistle of the wind.

In my experience, when used with "wind," "heavy" is close in meaning to "strong." In any case, the connotation of "heavy" in this context is also generally not positive. That does not really work here, because you said that it was "a little wind."

"Even if there is a little wind" suggests that you are going to describe something that normally happens when there is no wind. "Even" here introduces something that is slightly opposite from whichever scenario that has been set as an example or baseline. "Even if there is little wind" may work. Here is more context on the difference: https://dictionary.cambridge.org/us/grammar/british-grammar/little-a-little-few-a-few

And as long as you openleave the window for a small gapslightly open, you can feel the wind flowing.

"Open the window a little" also works, but I don't like it as much because "a little" can be interpreted in other ways.

All the staff of the company are serious and responsible,; they keep our community tidy and clear.

Unless there is a strong parallel between structures, in which case it may be acceptable for stylistic reasons, commas should not be used to separate independent clauses.

The community I live in is so ordinary, but I think it ishould be a good community in our city.

"should be" would mean it is not a good community, but you think it would be nice if it was a good community

The main reason is that it has a low rate of capacitysmall population.

you could also say "small population density" to mean the people are very spread apart from each other

It is not a businesscompany housing, but it was built by all of the company’s staff.

And as long as you open the window for a small gapa tiny bit, you can feel the wind flowing.

you could also say "as long as you crack the window, ..."

My apartment is cheaper than most but it is very comfortable to live in.

when you write "-er," it sounds more natural to compare the apartment to something specific
you could also write "My apartment is on the cheap side, but..." or "My apartment is not very expensive, but..."