1) If I receive the land owned by my mother as a gift, can I sell it off immediately and still it is counted as long-term capital gain? 

Yes Period od holding of your mother will also be included and if the sum period of holding is more then 36 months , It wiil be treated as Long term capital gain and hence taxable @ 20%

2) My wife is not working. Now let's say I utilize all the money (received by selling the land gifted to me) in paying off the land loan AND constructing a house on the property (jointly held by myself and my wife) - all within 2 years. Can I offset the long-term capital gain (from selling the property gifted to me) with the capital investment (paying off the outstanding loan, and constructing the house)?

Yes you can claim exemption u/s 54

3) Can I claim full tax benefit on the home loan paid so far?

yes you can claim the full amount as exemption  u/s 80C

Appreciate your inputs in this regard. Thanks a lot.

Regards,

Bikram

Dear Manmohan,

Thank you very much. That was very useful.

Regards,

Bikram

Regarding ur third que,,,u will get the benifit of sec 80C for loans principal amt...regarding interest..u will get benefit under section 24..........

Interest on loan taken for land cannot be allowed in sec 24(b) as section 24(b) allows interest loan taken for House property and land is not covered in definition of House Property. 

If House had been constructed on that land then interest on loan taken can be allowed