In addition to alastor933’s points, the Finder’s ‘make’ command has an unusual optional ‘to’ parameter, which can be used to set the target of a new Finder Window or alias file:
set targetPosix to "Users/rich/Projects/Project Receipts TBA"
set targetFolder to POSIX file targetPosix
tell application "Finder" to make new Finder window to targetFolder
Also, of course, you can simply tell the Finder to open the folder:
set targetPosix to "Users/rich/Projects/Project Receipts TBA"
set targetFolder to POSIX file targetPosix
tell application "Finder" to open targetFolder