Depends on the complexity of the DVD you need. You could just burn it from FCPX couldn't you? I know you could in FCP7 if all you want is the world's most basic menu and a single program. Never messed with Toast to actually author. DVD Studio Pro can make good DVDs if you travel back in time but Adobe Encore has always kicked its ass. If you have the Adobe CC suite you can still download the last edition of Encore for free and it still works even on the most modern Macs. Just be aware that you are making Tim Cook and Steve Jobs' soul very very angry by burning a DVD.
BTW my advice for Encore is to not let it encode your files itself. Make your own .m2vs and .ac3s with Compressor and import them.
There's all sorts of tricks when it comes to using Toast the most important is the encode bitstream rate.
A DVD holds 2 hours content playing at normal rate. I make my discs at max bitrate of 9.0 which means a disc only holds 1 hr video content, Use a 8GB dual layer disc if it runs over an hour to maintain the 9mbps stream rate. I do this particularly for 8mm/16mm movie film transfers from 1080 ProRes 442 files. Same thing for Bluray discs... Normal stream rate 16mbps but boosted to 26mbps. Make sure deinterlace is selected.
Menu selection in Toast is rather juvenile but there's ways to dress things up there by changing the background image and even modifying the layered .psd files within the app package itself.
1. Consider installing an older version of MacOS X in a virtual machine (one of the commercial ones), along with DVD Studio Pro and DVDEdit (or Encore). Make your video and audio assets (and graphics) in your current setup, then move them to the VM and build your DVD.
2. Create your assets and then have the manufacturer of the DVDs put together the disc itself. All responsibility for QA, etc., will rest with them.
I'm not sure, myself, if the hassle is worth it to try to deal with older applications. Why not oversee things and let the fabricator do the "dirty work"?
Believe it or not I freelance for a studio whose clientele insists on DVD's (parent copies of wedding videos). I have a working 2005 MBP with DVD Studio installed for this purpose. Let me know what you need maybe I can help.