Syntax and tense

The first line is written correctly?

should I add an "a" before cyber challenge?

3. Is it written correctly? come to try and break through the system (hacking)

The war between hackers and programmers escalates and becomes an official competition. I saw that there is a kind of cyber challenge, and whoever wins it, gets 100,000$. We, of course, suggested that everyone come to try and break through the system, but we said in advance that the system can not be hacked.