So I have a couple questions as someone whos new to pens. I see the V4 Ultra seems to be the top pick here. So with that here's my questions

1. where do you get the needles for it?
2. can I prefill cartridges and just switch them out in the same pen when I want to use different peptides or do I need a whole different pen? Do the extra cartridges have caps for this to be possible?
3. do you store the whole pen in the fridge between uses?
4. is a pen cheaper than disposal syringes in the long run?
   Thank you in advance!!