501c(3): SW Trails will be the fiscal sponsor and board to bootstrap SW Portland Tool Library for a small percentage of donations to cover overhead. SW Trails' donation site and EIN information can be found here.
There was also interest in storing and perhaps lending the SW Trails tools.

In speaking with the NEPTL they started with a similar arrangement initially out of a neighborhood organization, and did not have their own 501c(3) until 2018. The East Portland Tool Library similarly is starting under a fiscal sponsor.

Grants received (and very much appreciated):

Finance/Grant notes:

Consumables: Interest in how other libraries deal with this. Discussion on options, handy to make some available, but need to set cost. Cheap safety gear (glasses, masks, gloves?) would encourage safe tool use.

Sponsors (possible): Aboy, Parr Lumber, other (non-tool oriented) businesses (Lucky Lab?)

Software: Tool Librarian splits hosting cost for SaaS between all libraries, so our portion is ~$72. Concerns about long-term maintenance of software and arrangement, but otherwise price and features are fair. In use by NE/SE/E/Green Lents libraries.
No tool reservations in the software. Seattle Tool Library has 2hr reservation to allow users commute time to pick up tools.
Our Tool Librarian Admin Instance Tool Librarian Docs

Commercial SaaS equivalent: MyTurn (in use by NPTL and Portland's KitchenShare.org)
Possible open source software to base a solution on: Koha