Android here too so I'm going to have the best information to share
I rode my '07 GSA to Alaska (10K miles in 5 weeks) and rented a KLR in South America for several miles and weeks.
I started on a KLR and quickly realized I wanted a larger and more comfortable bike for the long hours on asphalt when not playing in the dirt hence the GSA.
I've been riding a day or two but predominately on the street so the dirt was a new experience (if I'm being honest with myself). I went to Rich Oliver's Mystery School (twice) and had a blast each time and look forward to attending again. I used the skill I learned there on a TTR 125 and 230 on my GSA. I believe you can attend less and more expensive training and get quite a bit of knowledge that will help when handling these large beasts in the dirt and other fun surfaces.
Be honest with yourself, do not get in over your head and try to ride with someone who is a better rider than yourself. Learn techniques to pick up the bike, work on it with the tools you plan on carrying, invest in a pump and plug kit and consider soft luggage if getting into serious off-road environments.
Gear...there are a few schools of thought here. I've got a two-piece Darien from Aerostich. It works but could be better. Klim is nice but almost too much for me yet I would not turn it down. I'm now leaning toward wearing body armor with a shell (Mosko Moto) for several reasons. When it gets hot the shell can come off and I'm still protected, the armor won't move away from where it needs to protect and more mobility.
Helmet....I like the peak on the ADV helmets not only because of the look but also the use when riding into the sun but by no means need one.
Get on the ADVRider forum if you haven't already. The wealth of knowledge is astonishing....you know similar to what you find here on BARF
What other questions do you have?
Sam