In some areas (NYC being one of them) there is a partial and full certificate of occupancy.

You can use a company like Cleartosell.com which will certify the tax deed (for around $2700 and 3 weeks)  and certain underwriters will be willing to insure the title based on their certification.  

They said for now if I pay the $5k I will receive a tax lien certificate.

There may be some slight changes since the official counts come out after all certificates are paid.Number of liens sold to investors:2016 - 1,880 (1,600 bought by investors - 280 Struck to County as no bidders)2015 - 2,039 (1,808 bought by investors - because 231 struck to county as no bidders)2014 - 2,5752013 - 2,382Total dollar of liens sold:2016 - $1,874,010.88  ( $1,694,277.89 bought by investors and $179,732.99 not sold)2015 - $2,678,533.35 ($2,336,551.03 bought by investors - $341,982.32 not sold)2014 - $3,015,871.872013 - $3,435,014.32Average rate of return overall:2016 - 6.28% (5.25% by investors when subtracting out struck to county liens which all get 16%)2015 - 6.75% (5.40% by investors when subtracting out struck to county liens which all get 16%)2014 - 5.86%2013 - 6.55%Number of Investors who won liens:2016 - 742015 - 89 2014 - 1162013 - 201Total Number of bids for all liens:2016 - 8,8232015 - 10,5252014 - 18,8122013 - 99,073,789You bid down the interest rate in 1% increments from 16% down to 0%.

County tax collectors office for tax certificates

Of course there were a number of rejects and we were given until mid Jan. to complete the work, -amongst the items a lead clearance, -in order to get a certificate of compliance.

Right now I am leaning towards tax certificates and tax deeds, Fix and Flip, as well as Buy and Hold.  

A house for $7k is probably not in livable condition and may not even have a certificate of occupancy, so you wouldn't even be able to live there while doing the work.  

I heard of withholding certificate maybe this is something that I should apply to reduce tax liabilitiesDo you know if I can claim all cost associated with business trip I will make to aquire hold and sell property for tax purpose?

A divorce, a foreclosure, a bankruptcy, a death certificate, etc.