A:AnswerYou should be able to upgrade the GPU. The desktop comes with a 500 watt power supply. You would need a 650 watt power supply to run the RTX2080 card. For further assistance, I would recommend reaching out to the Geek Squad at Best Buy.
A:AnswerIt has (At least mine does) 1 display port, 1 DVI port, and 1 HDMI port. So you should be able to actually hook up and run up to 3 monitors at one time. So to answer your question. Yes you should have no problem running 2 monitors.
A:AnswerHere are the expansion slots that are available on this desktop: 1-PCIe x16 and 2 -M.2 (typically used for M.2 solid state drives). On this link, it will show you the processor upgrade info: https://support.hp.com/us-en/document/c06330185