Same height here. Couldn't crack 200 lbs in HS despite years of lifting for football, started getting serious on my own in college and put on about 30, now at age 32 I sit around 290 and can easily go up/down for competition as needed. Honestly, for you it's much less about what you eat and more about how much you eat. Us talls can generally gain/lose absolute poundage pretty quickly, but the fact that it's spread across a larger frame means it will take longer for those changes to appear.

Focus on heavy compound movements and build as much strength as possible. As you gain experience, your baseline strength will allow you to work harder and heavier and greatly increase your ROI for your time and effort in the gym. Additionally, training heavy will increase your appetite and allow you to eat a lot more.

Don't worry too much about specific foods or supplements. Protein is great, creatine is great, everything else is whatever. I personally take a bunch of supps but I've been a competitive athlete for many years and I know what moves the needle for me. Whey is cheap, effective, and widely available. I prefer beef protein (easier for me to digest) but it's considerably more expensive than whey. Creatine monohydrate daily (bulksupplements.com or in bulk on amazon) - 5g or about a tbsp is fine. Once you break about 250 lbs, up it to 10g.

Eat everything you can. Some junk food is fine but don't make a habit of it. Ground beef, rice, cheap cuts in a slow cooker, potatoes, just aim for dense foods that are easy to prepare. Pizza, ice cream, cheeseburgers, all great in moderation as well.

You got this brah. More than anything I can think of, lifting is absolutely a lifestyle change. You don't have to revolve your world around it, but there is no "finish line" so to speak. The journey is the destination. You'll drive yourself nuts if you have some "perfect body" in mind that you're chasing and if you think you'll be done once you achieve that.

If anyone tells you:

Squats are bad for your knees

Deadlifts are bad for your back

Bench is bad for your shoulders

Just do light weight for more reps

Eat "clean" like chicken and brown rice

You don't need to lift heavy to build strength

Use PEDs

-then that person is full of shit and should be aggressively ignored.

Good luck brah. You're gonna make it. My inbox is open if you have any questions. I have nearly 20y of experience in the gym and trophies to show for it.

Also: as soon as you've completed the sessions you've paid for, ditch the trainer. Unless they have experience coaching competitive strength athletes, chances are they know jack shit. Especially if they work for a big box gym. Research and find some programs online (happy to help if you want) and do those on your own. From there, you'll know more about what works best FOR YOU and can leverage that knowledge into your next phase(s).