Hello vamshi,

Yes you can prepare both B.Arch and B.Tech entrance exams both in the same year and you can write both these exams. You have two attempts to write the exams. 

One in January and another in Aprill

Yes you can prepare for both

The jee mains paper 2 is based on mathematics, analytical reasoning and drawing. The test consists of three parts -

PART I - 30 objective type questions of mathematics consisting of 4 marks for each response.

PART II - Aptitude test has 50 objective questions consisting of 4 marks for each response

PART III - consists of 2 questions based on drawing carries 70 marks

So drawing is the easiest part to score 70 marks. Concentrate on analytical reasoning.

I think Arihant self study guide for B.Arch entrance examination can help you with the paper pattern and also your drawing.