I need to create a large image (for print) at 24X36 inches. It is a seating chart poster for a wedding. What settings in Photoshop would I set for an image this size (DPI, etc.)? I would need it to remain sharp when printing so suggesting some Export options would be great too.
It will be inkjet printed, so 300 ppi will give you plenty of quality. If the file size on disk gets excessive, 150 ppi would also be fine, but for a seating chart that's unlikely to be an issue.
Export to ("Save As...") PDF using "High Quality Print" as the preset, and you'll be fine for printing at your local FedEx/Kinko, etc., or on a desktop printer if you have one that will print 24" paper. Uncheck "Preserve Photoshop Editing Capabilities" to keep the file size down (but don't save over your PSD, just in case!).
If you're taking it to a digital print shop, ask them if they prefer the PDF in RGB or CMYK. If they say CMYK, use "PDF/X-1a:2001" as your PDF export preset. Otherwise use "High Quality Print."