I am filing a lien on a company that owes us both base totals of $228 and unpaid retainage of $273k, totaling $501k. Can I file this as one Mechanic's lien amount of $501k or do I need to file a Mechanic's lien on only the $228k and then a notice of unpaid retainage on the $273k?
You really need to retain a construction attorney to evaluate your situation, and to provide advice.
You do not indicate what work you performed, and when you performed it. Filing an invalid mechanic's lien could violate the Texas Fraudulent Lien Act, and subject you to statutory damages of $10,000, or actual damages, whichever is greater, plus attorney's fees.
To answer your question, a claim for retainage can be coupled with a claim for a progress payment under the appropriate circumstances. Sometimes, the claim for a progress payment is no longer legally available (due to lack of or untimely notice), and only a claim for retainage is appropriate.
Good luck.