Black oil sunflower seeds (aka BOSS) was kind of a BIG DEAL around 20 years ago or so. Everybody was feeding them. They do give the coat an excellent gloss, and the hulls are not a problem at all. But, nutrient profile wise, BOSS has some issues, and isn't always the best approach to achieve a good vita:min balance.
I would caution against feeding haylage. **SOME** haylage, such as the bagged alfalfa haylage Chaffehaye, is good for horses, but your typical plastic wrapped (different than net wrapped!) high-moisture round bales that are widely available in the OP's area as a form of cattle feed, ARE NOT safe for horses.
You might talk to the vet about dosing with a wormer with Praziquantel in it, now that a hard freeze has hit. Praziquantel will take care of tapeworms. Praziquantel is usually in a tube with an ivermectin product: Equimax, Zimectrin Gold, etc. You can also find it with Quest (moxidectin) but you really need to talk to your vet before using Quest. It is a different class of wormer and not always the safest choice for every horse.