You have below a list of symptoms present in MPNs, ET included. Several other studies found that risk score and symptom severity are not necessarily overlapping, meaning that it is possible for someone diagnosed as low-risk ET to experience a lot of symptoms.
"Prominent symptoms include fatigue (92.7%), early satiety (61.9%), abdominal pain (45.9%), abdominal discomfort (53.2%), inactivity (60.5%), headache (48.3%), concentration problems (61.7%), dizziness (55.2%), numbness (61.3%), insomnia (65.4%), sad mood (62.7%), sexuality problems (57.9%), cough (46.4%), night sweats (56.4%), itching (52.6%), bone pain (48.5%), fever (20.2%), weight loss (34.2%), and impaired quality of life (84.2%)."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC46...

This is a nice summary of ET symptoms and their potential cause:
https://www.voicesofmpn.com/essential-thrombocy...

Regarding bone pain, an explanation can be the following:

"In normal people bone marrow is confined to the central skeleton (cranium, ribs, sternum, vertebrae, and pelvis). The long bones contain mostly fat. In MPN, the bone marrow expands outward to the long bones and can be seen even out in the fingers and toes when bone marrow scanning is done.
The proliferation within the bone marrow cavity may cause pressure inside the bone that, in turn, causes inflammation of the covering of the bone (periostium).
The resulting periostitis may be painful. In some patients with bone and joint pain treatment with myelosuppressive therapy has decreased or eliminated these symptoms by reducing the amount of bone marrow in the cavity and reducing the pressure that it causes."
https://www.pvreporter.com/bone-joint-pain-mpn-...

Hope this information answers your questions.

Essential Thrombocythemia Symptoms

https://www.voicesofmpn.com/essential-thrombocythemia-symptoms

Bone & Joint Pain In MPN Patients Explained | Proliferative | PV Reporter

https://www.pvreporter.com/bone-joint-pain-mpn-explained/

Impact of Inflammation on Myeloproliferative Neoplasm Symptom Development

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4619953/

I've had night (and day) sweats for several years. I'm sure it's related to my ET, because I'm way past menopause, and I've been off Hydroxyurea for about a year and a half.
I've dubbed my episodes SINS (sleep-interrupting night sweats). I have them about every two to three nights. Although they're hugely annoying, they're neither painful nor life-alterating for me.

I’ve had night sweats since I started on Jakafi. Some nights I even have to change clothes.

I have had them. Not as much since the colder winter weather as we keep the temp set at 67⁰ over night. But when it warms up, I'm sure they will return.

No, I have never had night sweats until just recently. I noticed they happen the day after I take Fosamax. Which could be just coincidental.