I think you're doing the right thing and you have gotten a lot of sage advice so far. Come back with truck details and folks will provide you with more information than you probably want to hear. You really are on the heavy side and I doubt you would be comfortable pulling that trailer.
As far as the slide issue is concerned, we have a similar design in a different trailer. It hasn't really been a problem for us. We just put out the pax side slide a foot or so and we have access to both the fridge and bath. Takes about 15 seconds. Yours may be more complicated than that. However, I guarantee you'll appreciate every slide you have while you are parked in a campground. They make a huge difference in interior space.
Don't trust the dealer or the salesman. Most are not very knowledgeable about towing factors and have never towed an RV. They are probably not intentionally trying to lie to you, they just don't know any better. They sell trailers, they don't necessarily use trailers.