@ Ali Bodla
well bro it depends on ur choice.for css preparation u should study atleast for 6-7 hours a day.if u can manage this time with job u can prepare for exam along with ur job.infact concentration matters more for preparation than how many hours u study.
for ur second question it is also ur choice.but guidance is must for this exam in my opinion.this forum will also provide u alot of guidance.don't rely on the academies only they will provide u only guideline.if u need it go for one otherwise u can prepare well at home.
Good luck