Welcome to Connect, @jtcat7. Looks like you have a full deck of mutations in your hand. Over our lifetime, we can develop some genetic mutations. Some of these may lead to various blood disorders such as myeloproliferative neoplasms (MPNs) which can cause issues with our bone marrow and its ability to produce healthy blood products. Many people with MPNs have either Polycythemia Vera (too many red blood cells) or Essential thrombocythemia (too many platelets). Both of these conditions may rarely progress to MF. MF (myelofibrosis) the normally spongy bone marrow can become filled with scar tissue or fibrotic tissue and interfere with blood cell production.

You’ve asked a couple of questions regarding the speed of progression and how you can feel if you’re moving from pre to the next phase. Those are great questions for your hematologist.

I did find a good series with videos from Patient Power with information about MPNs and prefibrotic primary myelofibrosis which might help in answering your questions.
https://www.patientpower.info/video/myeloproliferative-neoplasms/treatments/what-is-prefibrotic-primary-myelofibrosis
Was your high platelet level discovered during a routine exam or were you having any symptoms that to the discovery? How are you feeling with the HU? Any side effects?