Iv found several useful keywords in domain names which have yet to be taken, however iv already bought a domain name and want to use this as it gets slightly more hits, can I also have the other domain name and have it point to my main site. Incendently the keywords differ greatly but my site is relevant for those keywords so would this be allowed. So for instance say I had a website selling books and the second domain I bought was to do with book forums could i link them. Example : Bookforums.com linking to buybooks.com which contains a book forum as an example.
I suggest use sub domain for one of your topic.. You can use bookforums as sub domain like bookforums.buybooks.com..
Buying lots of domain names can and can't affect your SEO CAN'T - if you just buy book-forum.com and forward it to about-books.com Google will ignore the first one and it won't rank. CAN - if you buy about-books.com but also buy about-books.co.uk the many visitors who know your site but type the domain name incorrectly will find your site and you will have more visitors. If you have more visitors Google knows about it and will rank about-books.com higher
There is nothing wrong with having multiple Domains for a single site. Under the condition that only 1 of those Domains resolves directly to the site. That means you should have a Preferred DomainName. If anyone requests the Preferred DomainName, they should go directly to the site - getting a 200 response. All the other DomainNames should point to the Preferred DomainName - using 301 Redirects.