The tincture and vinegar ratios look good with that strength. After you harvest the leaves/aerial parts, either let them wilt to draw the water out of them for 12-15 hours or wait until they are totally dry. Too much water will cause the oil to go rancid faster. Cut the horsetail up into smaller pieces, place in a mason jar (3/4 full), and then top up with your oil of choice. You can also add in vitamin E oil or rosemary oleoresin for preservation. You can put this in the slow cooker on low heat for 24-48 hours, then strain.
I love using olive or avocado oil for warm infusions, as they are more stable with heat! You could also do a blend with jojoba oil.
If you wanted to add other herbs in, nettle and rosemary pair great with horsetail (for hair strength and growth). If you plan on using this oil for your face, you could add in some rosehip oil and rose geranium essential oil.