I am wanting to remain as anonymous as possible and please wondered would it be okay to use a VPN to mask my real IP address when using Bisq please, would this still work please?
As bisq is run over Tor, it makes it unnecessary to use a VPN as well. It's also very easy for you to make a mistake while using a VPN and unintentionally make yourself less anonymous. Best to stick to Tor.
Lastly i have heard about people setting up there own nodes on Bisq, would this make the transaction more anonymous or is this basically to keep the transaction more secure so you do not get scammed please?
Your own node makes you more anonymous (and nut more secure).
It doesn't matter if youreonly trading $40 now. If you plan to make future trades and care deeply about anonymity, you should consider running your own node.