Yes, you can pursue child support through CSE without filing for divorce. The pro is that you would, hopefully, start receiving some child support. The con is that he might file something asking for parenting time with the children.
Lawyers can provide advice away from the courtroom and assistance in drafting documents without becoming your lawyer for the entire case. Those are called "unbundled services." I suppose some lawyers are willing to do "slow pay," but I am not one of them. You might be able to obtain pro bone representation through CU's law school, DU's law school, or Colorado Legal Services. Whether those entities provide good advice depends on who they assign to the case. You can get both good and bad advice from a privately paid attorney, too.
You will need to understand that if he wants a relationship with his children, the court will give him an opportunity to have a relationship, unless you can show that he is an actual danger TO THE CHILDREN. Courts are not going to allow your children to testify in your divorce. If they have something to say, the Judge might, upon proper motion, interview them in chambers; although, most Judges I have known over the years will not conduct such an interview. Or, you can ask the court to appoint a Child and Family Investigator. If you qualify as indigent, the state will pay your portion of that person's fees. The CFI will talk to the children and let the court know, through the CFI's report, what the children say. However, children do not get to decide whether they have contact, or what kind of contact they have, with the other parent.
www.karlgeil.com. This answer is provided as general information about a legal issue, is not legal advice specific to a particular case, and does not create a lawyer-client relationship with the person asking the question.