I played clarinet for a while before switching to French Horn, (I am now learning trumpet as well) - the general theory for brass instruments is the same so I should be able to offer some advice.
Compared to F Horn, trumpet is EASY, I'm loving it! Compared to clarinet, trumpet is different, but not necessarily harder. Some people are just natural at brass instruments, others really struggle. I found the most difficult thing about brass in the beginning, was switching embouchure's from clarinet to brass.
The trumpet itself takes alot more air than the clarinet, especially in the higher octaves, but the fingerings for instance are REALLY easy compared to the clarinet.
I've sent you a PM, if you want extra help