on facetime, can i change the email and phone number that i use?
email yes,
phone, no, unless you have another activated sim card laying around. the ipad does not support phone number imessaging at this time
im currently using landline number and personal email
How are you using a lan line with your iphone?
your email will always need to be an apple id. that being said, once you sign up for icloud you recieve an @me account and five other aliases you can create from it.
would i be able to change to a mobile number and gmail?
sure, if the mobile number is the one for your sim card and the gmail account is your apple id. this is stictly apple id communication. Create an alias with your me.com account and use that.
is there anyway to block my details and keep them private so they dont show on facetime
No. In this case, you're better off not giving them your phone number and email address because one of the two need to be given to generate a facetime call.