Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
If you take a land loan and do not build right away, the interest on the land is not deductible in the year paid but gets added to the cost of the property which will serve to reduce your gain at some time in the future when it is sold.
If you take a home equity loan against your house the interest will be deductible on your tax returns in the year in which the interest is paid. That seems like a more feasible approach.
As a minor aside, raw unimproved land is taxed lower than improved land. So for now that is a lower cost way to go (for property taxes). You may also wish to look into someday getting the land deemed a farm when you build on it. Farms have lower property tax rates than residential property. You will need to check on local regulations for that.
The limit is $100,000 ($50,000 if married filing separate.This limit is imposed on the debt itself. So if you have a home equity loan for $125,000 then 80% of the interest is deductible (100,000/125000=.8 or 80%).