asking permission to use the mod - forget it, your in fantasy land. a free mod for free download to the public carries no such obligation. asking modders to do this will discourage the sharing of new mods that didn't go to all that trouble.
as for a modder including an email addy for contact - get real, who wants tons of spam and repetative emails every day not to mention the occasional critic.
stating that if this mod is used then proper credit must be given to me and john doe is the reasonable thing to add in your mod code.
it's a good idea to REQUEST that it state this mod is or is not based on realism
as for mods without credits or read me i say anything out there is fair game and free to use without restrictions on how you use it. contrary to some views i have read, it is not my obligation to spend my time and effort searching for a modder who did not include the info i need to credit him when he made his mod download. i will give him full credit as best as i am able to but i would not lose sleep worrying that i couldn't contact him for permission unless the read me stated specifically that request.
i think we are going too far into the minutia of the credit issue where we should look more at helping the modders made their mods better with read me's that explain just what the mod does, any credits given as needed, and what i see lacking in most mods is a date and/or a version number for the mod.
please lets go this route with this post and not lock in on who gets credit.