Law / Citizenship by Descent from Polish Grandfather [NEW]

Hi all

I have a few questions about this. If anyone could help, that would be really appreciated. My grandfather was born in Poland in the 1920s and naturalised in England in the 1960's after fighting in WWII. I understand that I need to gather various documents such as birth certificates and send them off with the application to the Polish embassy. I currently have zero documents so they would all have to be retrieved from archives.

Will there be any problems due to my grandfather having fought in WWII?

What about naturalisation in England, does that affect the process?

Do you have to go to Poland to get documents from the archives?

Apparently there are paid services that can do all this for you, are they good and can you recommend any?

Thanks
Tadeusz