Hi,
First of all I would like to tell you that it is just my opinion in case of SEO. Redirecting a sepaarte domain into subdomain of new website wouldn't be a good move and neither I have heard something like that so far. Wait for some other community member opinion/suggestion on this.
In case of Adwords I assure you that there is no need to create separate Adwords account. First of all check for double serving because you can't have two adwords account to sale same products otherwise your account could be banned by Google adwords. If that is not the case you can create separate campaign in existing adwords account instead of creating new adwords account.
Thanks