Ok, keep it cool until you have the funds then do it to ease your mind

Hire a PI then you will know. Don’t bring it up again until time passes so your wife will think everything is ok and let her guard down

Seek therapy immediately, your wife has been using you all this time. Always remember that DNA doesn’t make a father the actions of the person makes a good father. You can still be a great dad but divorced from your serial cheating wife