Actually Both are very good.

Architects are to design whole Interior and Exterior structure of a building including electric connection and plumbing connection, ceiling and flooring pans, Also it is based on styling External look.

Interior designers are majorly for Styling the interior parts of a building or home. All finishing plans , painting plans, backsplashes, lighting plans, furnishing plans and placement of windows is done by them.

choose according to your interest (note : Both has their major markets)

For good institutes and better salaries, Abroad is better, cities like Norway, panama, brazil etc, offering more jobs for architects and interior designers. Now a days in India also payouts are increasing as many rural and urban areas under development are increasing. If you can afford go for abroad or Choose India it is also good.

Hope this answered your first question

No need to Crack JEE for NATA, but if u crack only nata then you can go only for some private colleges and some colleges under architecture association. If you crack JEE B.Arch you can apply for IITs and other major colleges.

All the Best!