Hi i am trying to build a salesforce1 app with all custom objects/tabs
. Can i remove standard tabs like accounts/contacts... objects from
Is it possible to remove salesforce1 standard tabs??
You can remove tabs like "Today" and "Tasks" by using Setup > Mobile Configuration > Mobile Navigation, but Accounts and Contacts can only be removed by removing the user's ability to view those objects/tabs entirely. Those tabs naturally move towards the top as the user uses these tabs, so the app customizes itself for each user based on their usage.
I am having second question: I am using a complete new layout page
which is designed using vf page and i added it to button(tab/view
page) but in salesforce1 i am not getting standard pages. Can i
override new vf page in salesforce1 for standard objects??
Yes, but the Visualforce page must be marked as "available for salesforce mobile apps", or it won't override the page. You can view this setting by editing the page in the browser, or by viewing its property file in the IDE.