Hi and welcome to TONMO.com!
You need to read some of our Ceph Care articles to get more information about keeping an octopus. Click on the Ceph Care button above, and have a look at the Bimac Care Sheet, the Equipment List, and the Checklist, for a start.
We're recommending 50 gallon tanks for bimacs - some of them get larger, and a 30 is a little cramped.
Yes, you can gain the trust of your octopus and touch it. Actually, they like to be petted. My bimac liked to be rubbed under her eyes. (The first time you touch each other, it's likely to scare both of you!) Here is a pic of me touching Ollie.
If you don't have a sump and your equipment is hang on (and yes, you have to have a protein skimmer), it's harder to seal the tank. You may have to work with acrylic and duct tape, allowing some ventilation (maybe covering that area with mesh).
Nancy