If I was transfer my website to a different domain, would the pointing of DNS still be done from the VPS cPanel which my hosting provider has?
You just point the DNS to the IP address of your VPS. It will direct to htdocs
2. Does VPS really significantly improve my website's loading time even if it is using high quality photos?
Not really. Load time is dependant on optimization of your website in most cases. You will start noticing it slow down when you have a load of traffic going to it. But it's already slow with no visitors, its probably the wordpress theme or plugins causing that.
3. Since it is a Virtual Private Server, does that mean I could be hosting two different site at once? And does that affect my other website's performance if I was to run another website in the exact same server?
Yes. You can host as many sites as you want. Aslong as you have domains, you will just need to point to the right address. Heres a link explaining it,
https://stackoverflow.com/questions/...g-only-one-vps
Also check out this website to see whats causing such slow load times. Bookmark this website, its really helpful
https://gtmetrix.com/