Are Apartment with set back deviations safe for investment? how much value of apartment is should you give in cash payment.

Q: I have shortlisted an apartment; builder has taken setback deviation; as per approved BBMP plan he has to leave ~3.17M front, ~2.5M side/back instead builder left has left only 4 feet on all side, such that apartment balcony projection is matched to road edge. and also there are deviations form sanctioned plan in total area of individual apartment . Are these a major problem, can I finalize the apartment? Builders quotes more than 90% apartments are like this only so no problem.
Builder told he'll get project approval letter form LIC, if LIC is approving the project, is my investment/purchase safe.
The apartment is half constructed n builder says Dec 2012 as completion date,also Builder is asking for upfront 50% i.e 15 lac(10 cash+5 cheque) and remaining at the time of registration. Is it safe to give that much cash to builder based on agreement.