Reddit mentions of Rubank Elementary Method - Cornet or Trumpet (Rubank Educational Library)

I'm usually against people starting trumpet late. But you have some background in music, can read music, and even better, have a little wind playing background.

Trumpet is a harsh mistress though to a hobbyist who has a busy life outside of music. Like Felt_Ninja said, and the primary reason I tell people not to play trumpet as hobbyist, the trumpet requires maintenance practice. It's too damned easy to fall off the horse on that when you have other priorities. Skipping a day, then two, turns into a week and then suddenly you essentially have to start from square one.

Trumpet is like marathon training. You can know how to run, but you have to train consistently. If you take a week or more off, you're endurance and everything else goes out the window. Luckily, you retain the knowledge and the muscle memory, but it can be frustrating to start back from scratch.

I can recover from a 2+week hiatus in 1 week for absolute utility playing, but more like 2 weeks for really solid playing. But that also has to do with the fact that I know exactly what to do to get back in shape based on decades of experience. It's not uncommon to see threads here or run into students who try to jump back in after a summer off and literally have no idea why their playing suddenly sucks and why they can't do what they did before.

So if you don't think you can keep at it very consistently, I highly recommend another instrument. Saxophone is usually my go-to suggestion. It's the easiest hobbyist melodic instrument. It requires almost no maintenance. My wife could take 3 months off, get called for a gig, and play that night pretty solidly on sax (or pretty much any other woodwind except flute). No trumpet player can do that. So if you foresee interruptions happening in your life that don't allow you to consistently be practicing at least 30 minute every day with no more than a day or two off here and there... stay away from trumpet. Clarinet is another easy option if you like that sound. Then the most you have to do is maintain reeds and you could easily get something like Rico Plasticovers to make that even easier.

All that in consideration, if you do want to go for trumpet, I'd say lessons would be a must for a good while at the beginning. Making mistakes early on can lead to handicaps that are very hard to fix once you've practiced a bad habit.

The Rubank Elementary Method is my go-to for people who have some background and want to learn a secondary instrument. Actually, for almost any wind instrument, this is my recommendation. They move fairly quickly and they are great to work through while somewhat quickly adding range and technique stuff.

For hobbyists, if they can read well enough, I recommend getting something like iRealb and getting some fake books. You can turn on the band in a box and jam out to lots of songs. Hell, even if you are good enough with your scales to play by ear a little, you don't even need the fake books and you can download tons of stuff in the forums for pretty much anything... not just jazz, but pop and rock stuff.

For horn stuff, I think Felt_Ninja pretty much summed it up. You should almost always stay away from really cheap crap. You'll do much better getting a used horn of decent quality than a new, shoddy horn. Those instruments are practically disposable, most shops won't touch them, and they don't play super well.

When you're first first starting, like the first month or two, get one of the trumpet method books they use in elementary school.
http://www.amazon.com/Rubank-Elementary-Method-Trumpet-Educational/dp/1423444795/
It will help you with reading and sounding melodic. Practice going up and down intervals without changing fingerings. Then move on to wider interval patterns. Use only a small amount of pressure against your lips, even for higher notes. Do chromatic scales starting from different notes. I personally think Clarke's technical studies is a better starting point than Arban's for an absolute beginner.