Wash less frequently, the conventional shampoos usually strip the hair of its natural oils, so the scalp overproduces it, jut in case you decide to strip it off again 
i used to have oily hair too, and keeping a steady washing routine and dreads itself treated the problem; i now wash every 3-4 days and my hair is rarely oily.
Thats the spirit :D keep up the good work! And welcome!
I believe henna wouldn't hurt dreadlocks (altough i haven't tried for myself), it might only slow down the natural process of dreading, since i believe it's a bit conditioning.
I would suggest buying natural henna blocks, that most natural stores have. Those don't have any additives, that the pre-made ones may contain. Good luck and keep us updated with the results (:
None of the methods will make them look "socially acceptable"/neat, but they aren't supposed to be that way. They should be going wild and mingling with fellow neighbouring hair.
I suggest you to just take it easy and go neglect (:
I believe this works if your water is really hard. Our water is somewhere in the middle between extremely hard and soft, and as i tried that experiment, the dish washing soap foamed, but not as much as one would expect it to foam.
I hope this was helpful!
Dr. Bronners
Maylee's garden
Lush soaps
baking soda
Use the forum search options next time. it's really useful (:
