Forest Service Flexible Partnerships Act of 2017 This bill authorizes the Department of Agriculture (USDA) to lease as an administrative site, for consideration that is at least the market value of the site: any facility or improvement that was acquired or is used for the administration of the National Forest System (NFS); any federal land associated with such a facility or improvement that was acquired or is used for the administration of Forest Service activities and underlies or abuts such facility or improvement; or per fiscal year, no more than 10 isolated, undeveloped parcels no larger than 40 acres each. The bill makes the National Environmental Policy Act of 1969 applicable to the leasing of administrative sites, subject to an exception. Cash consideration for an administrative site shall be available to USDA to pay: necessary and incidental costs incurred in acquiring, improving, maintaining, reconstructing, or constructing a facility or improvement for the NFS and the lease of such site; and reasonable commissions or fees for brokerage services obtained regarding the lease.