if your going to get your cdl, you'll be better off to get the class a. And while your taking the written tests, you might as will get all the endorsements, even if you don't think you will need them. It can make it easier getting hired. Also, if you end up out of work you may need one of the endorsements to get hired somewhere else. If all you can get to take the test is a class b truck, go ahead with that and when you get hired, still try to get the class a eventually.
Sometimes it can be harder to get hired locally than otr. A lot of companies want 2 years otr experience. But it just depends on the company. Like mentioned above, talk with the teamsters. Your local may have an apprentice school that will train you and get you your cdl.
When I was 18, I started driving for a union construction company. I did good in apprentice school and became good friends with one of the instructors. When I turned 21, we both bought trucks and hauled oversize loads otr. I did that for 2 years. Then drove for halliburton in iraq and and a buddy leased my truck from me while I was gone. There are a LOT of opportunities driving. One thing you may find tho, is you usually can't be too picky untill you have some experience