As Krat said, defo have Caber on hand... Deca in any form can cause prolactin issues.
I believe Deca slightly increases synovial fluid production/secretion.
It is best to strop Tren/Deca before test on cycle but seeing as your Deca is in fast acting NPP form and your test is in the long enanthate form this should be all good for you anyway.
As far as Deca being good for joints, I have Psoriatic Arthritis and I did run Deca D a while ago at 250mg per week, from what I recal it did seem to help slightly but it could also have been many other variables and councidence.
My advice is just to try it out! You have obviously done some research and have your PCT ready. Get Caber at the ready, you could use it from the get go @ 0.25mg 2x per week with a max dose if you get the deca dick at 0.5mg 2x per week.
Did yoy use an AI and HCG during your cycle and still using them? I always ask if it isnt mentioned.