I have barely glanced at it myself, but there's an Assets starter solution for managing assets.
I suspect that adding barcode functionality and checking out an instrument to more than one student are both features that will require that you either modify an existing template or to create a new from "from scratch".
A few pointers: If you plant to get a barcode reader to attach to your computer, make sure that it works in "Keyboard emulation mode" (almost all do) and that there is a way to configure the scanner to append additional characters to the beginning and end of the scan. These added characters can be used to trip the OnLayoutKeystroke and onObjectExit triggers to automate what happens when you scan a bar code. Barcodes, by the way are just text printed in a barcode font so once you have scanned a barcode, the text it represents will automatically appear in the field that has the focus.
If a student can have more than one instrument checked out to them as well as more than one student checking out the same instrument, you have what is called a many to many relationship. You may want to research that issue and the supporting concepts of a "join table" and "portals" to gain background info on how to work with such a relationship.
The White Paper for FMP Novices is useful
Lynda dot com has Filemaker Videos (portions are free)
Free unlocked templates are useful for examining design
Starting Point -
A free calendar is available to be bolted onto your database
You can search specific Filemaker sites on this Custom Google Search
Looking at FMP business database demos is useful - some are fully useable
The Excelisys Business Tracker V3.0