Learn English – wanted to make sure vs wanted to be sure

Risking to express a controversial opinion, I would say that technical documentation has slightly different priorities than normal texts. Being in I.T., I read and write tons of technical papers, and I always prefer readability and text size versus formal grammar.

Think for a moment, your reader is often a non-native speaker as well, but, most certainly, they are a busy person. Overuse of large grammar constructs may just increase the size of your writing, without adding any value.

No, I don't say your document should be ungrammatical. Instead, it must be based on keywords, the shorter the better (unlike my answer :-)
Let's review individual phrases (I took those from your original edit):

• Description of the Project vs. Project Description — are you really sure that project is strongly necessary? If you leave just Description, wouldn't it make your documentation more succinct? I think, it would; There's also special terms, purpose and abstract to denote sections containing verbose description of a project and its rationale;
• Justification of the project — I wouldn't use justification at all. It has several meanings, and you may confuse your reader. Alternatively, it may be review, analysis, or clarification, depending on the context;
• Definition of the scope of the project — there's a term, Scope of Work;
• Bounding of the projects — use Special Requirements or Dependencies instead;
• Benefits of this proposal — just a keyword, benefits, seems to be sufficient (indeed, if not of this proposal, of what then?);
• Competitive Advantages — it's a term by itself, stick to it;
• Deliverables of the project — Deliverables and Artifacts are standard terms;
• Preliminary schedule of this project — just schedule. Everyone understands that it your schedule is proposed, therefore it is subject for change, and, because of that, is preliminary;

Summarizing:

• Use keywords, separate the wheat from the chaff;
• Use widely approved terminology, don't reinvent the wheel;

In some contexts, "to be careful" can be used to mean "I have an ongoing habit of making sure I do [x]". This is the case in your hand-washing example; "I'm very careful about washing my hands before eating" means "I always make sure to wash my hands before I eat".

It doesn't work quite the same way in a command, though. If you're telling someone to be careful about/while doing something, you're cautioning them. For example, "Be careful when you cross the street!" is said to make sure someone uses caution and isn't hit by a car, not to tell them to be sure to cross the street.

So, in your example sentence:

"Be careful of wearing a coat."

This doesn't mean "Be sure to wear a coat", but actually the opposite; it's a caution against wearing a coat. It would be understood as:

"Take caution when you wear a coat! When you wear coats bad things can happen, and you need to watch out."

Which is probably not what you mean to imply!