NOW I practice RCs maybe 5-10 a day. It became an habit.
This might be the reason why you're not achieving that many lucid dreams: if you turned them into a habit, then you should be doing way more, as there are dozens of cues every hour on practically any person's routine that might cause them to question their state of consciousness.

So my question is: Could RC alone produce LDs? If yes why? If no why?
Should I do more? Add another technique?
Yes, reality checks alone can produce lucid dreams, is just as good of a technique as any. Why? Because they are specifically designed you to achieve lucidity by wondering directly about it. In some ways, they're even more reliable than other principles that lucid dreamers tend to rely, since they dismiss any need of rationalization and put you straight into "action mode".

Regarding the use of other techniques, stick to the basics: dream recall and focus on the awareness that you might be dreaming at any time. The rest is all a matter of experimentation: see what interests you, check if it works (if not, readjust), and repeat it over and over ^^