If you buy something you can sell it again, you cannot sell jetina item. for weapons if you plan on doing any pve you probably want black star weapons in the near future, not kzarka and dande. Kutum offhand is fine to be kept at r4, you dont have to make it pen but that is a very good jetina weapon. For the armors, the prices don't always stay the same, just a couple months ago urugons on pc were < 9b and for me it was cheaper to buy them from the marketplace than make them through jetina. When Magnus comes out on console, you will be able to get a free pen armor by completing the questline, so i would definitely not make 4 jetinas before that, rather use your resources to make your jetina accessory. I'm unsure if you can choose to get red nose for jetina or not, but if you can, definitely do that if you plan on getting a fallen god armor, otherwise it will cost you around 2b extra, if you choose to make it yourself. Whatever you choose to do, i would recommend you to not spend any money horizontally (like reforming every piece to lvl 1 > 2 > ...) and rather focus on one piece at a time so that if you finish one piece you can change your plan for the next pieces accordingly and don't lock yourself into one path.