A mild soapy water solution, 1/2tsp. dish soap to a quart of water, would be just as effective and less harmful for your spider mites, Ben. Soap is the preferred treatment for most sucking insect problems on edible plants. You do need to treat every few days for a week or two, to get all the generations though, since the soap rinses off if it rains. Be sure to get all the leaf surfaces with the spray.
The dropping of yellowed leaves is certainly a sign of spider mites, and if the new growth looks good, you may have a handle on that, but use the milder remedy in future. Rubbing alcohol is used as a spot treatment on a Q-tip for mealybugs, but I would never spray it on a plant, even diluted.
A picture or pictures will be really helpful to diagnose the brown leaf problem, but off the top of my head, it might be nitrogen burn from the manure you used in your potting mix. Sometimes it releases too fast, or in fact all at once, and can give young plants too much to handle. That's the usual thing that causes brown leaf tips. It's a risk using manure in containers because you really don't know how much/how fast your plants are going to get the goodies. Better to use a controlled release pelleted fertilizer, or a soluble fert, at regular intervals in containers to prevent any chance of burning leaves, or later on, starving your plants because all the soluble nutrients were used up early by the plant.
