If you convert the footage to “Apple ProRes422” why are you using an (HQ) sequence setting.
You can down-convert the footage in FCP by dropping it onto a SD timeline. Keep frame rate and compressor codec the same.
Or when you take the HD QT export into Compressor turn on Frame Control and set to best (will take a lot longer to encode) If your money is under 90 minutes change the Encoding mode to CBR and set it to 6.5 Mbps. (this will short the time to encode).
All in all you need to do short test and burn to a disc.
Building menus in DVDSP sucks, especially when you use the text for highlights, build them in Photoshop or Motion. There are a number of threads in the DVDSP forum on using the correct size for menus.