This thread should provide some inspiration.
You've covered most of the obvious options: Accessory mount on the derailleur post. The derailleur post bottle cage bolts. The dynamo light mounting bolt on the underside of the boom (note that only works with lights that can be hung downwards, which eliminates most of the ones with B&M IQ-style optics prior to the IQ-X which is reversible, and the EDelux II which is available in an upside-down flavour). I'll also add the rider's head, which is useful but not legally compliant, and potentially on the fork using standard mounting-light-to-forks tactics, which is rubbish because you get silly shadows and end up lighting the bit of road you can't see because of your feet.
As you can probably gather, dynamo lights are going to be significantly easier, as all you need in addition to the standard fork crown mount is an M5 bolt and some washers. Some of them
[1] can potentially be powered by batteries if you want to be cheap/perverse about it. If you're going to use battery lights designed for handlebar mounting, then I'd go down the
accessory bar or
ICE front light mount route.
(For completeness, I should mention that In addition to the dynamo light in the photo I posted to that thread, I also have
a fork-crown mount designed for the B&M Ixon IQ on the upper bottle cage bolt. This is a sturdy mount that is compatible with the SMART front lights, as well as the Ixon. My Ixon broke years ago, but I stick a basic PlanetX Smart-clone on there as a backup for night rides.)
Obviously if you use the bottle cage mounts for lighting, you can't use them for bottles. This is no big deal, because it's a stupid place to put a bottle anyway. Unfortunately, one of the few things the Streetmachine is lacking is a sufficiency of places to mount bottles. The one under the boom below the seat works well (if a bit fussy about what cage you use if you have a lowrider rack), but you can't reach it while riding along. Some people drill the seat and attach a couple of bottle cages to the back (I've got this arrangement on my other recumbent). Some people give up on reaching bottles and use Camelbak-style hydration systems mounted on the back of the seat or luggage rack. You may be able to use a band-on bottle cage attachment on the top of the boom between the stem and the derailleur post. Personally, I use a bottle in the underseat cage (and make do with having to stop to reach it) for short rides, and a custom hydration bladder solution on the rear rack (hose magnetically secured to the underside of the seat) for longer rides.
[1] The B&M Cyo family will run on 7.5VDC. Various lights designed for e-bikes will run off a wide range of DC voltages. But you're into fettling battery packs if you go down that route.