Based on my own recent experiences with international flights with a toddler:
A 2-hour flight is rarely a problem; even in the worst scenario it's not long enough for you to lose your mind :-) I have no experience with longer flights with infants but I think 4 hours are still within reason, while 10 hours (transatlantic) could be a bigger challenge.
Sitting upright is something I'd recommend only for toddlers and older kids, especially for longer trips. Most 7-month infants can't sit upright on their own, because their back muscles and spine aren't adequately developed for the upright position. Infants should be placed in an infant seat (just like in the car) or lying flat on the back in a carry bag (used with the baby buggy) -- both would require it's own passenger seat on the airplane, and this does incur a ticket price.
Since you state that your child can indeed sit by himself (can he sit for four hours in a row?), you might decide to ease up on the general idea I just said. It's your child, so of course you know best.
Ears and the cabin air pressure:
Your concern is valid, and the experience varies. Some people (any age!) are very sensitive to cabin pressure changes; others barely notice. With infants, the best cure is to give them something to suck on, preferably their milk bottle, or water or watered-down tea (not black). The sucking motion will open canals to the ears that equalize the pressure -- adults sometimes chew gum to the same effect.
Take-off and landing:
With small children, the potential terror doesn't come from "oh no we're flying/gonna crash/etc." but rather from the unexpected sounds, especially after the fairly loud and very unfamiliar ordeal of getting through the airport and into the plane to begin with. I know no particularly good solution against the noise except for what I'd do concerning noisy equipment at home too: explain, talk, cuddle, soothe, sing, touch/caress -- whatever you've learned to work well with your child.
Off the top of my head:
- You might want to bring a new toy along, as an "emergency distraction" when you're out of options. Choose a kind of toy that the child already likes. Use it only for airplane/airport situations.
- Make sure your baby day bag is sensibly packed and that you're not low on any consumables like diapers, wipes, fruit bars, etc.
- Make sure you're allowed to bring all the items with you into the cabin, and consider printing out the airline's statement about this just in case there's any security trouble.
- Airports use the code
DAA (deliver at aircraft) to designate baggage that you can bring straight to the airplane and give to the flight attendants for stowing during flight; you'll get it back as soon as you leave the airplane. Make sure that both ends of your flight allow this. Again, bring printed documentation in case there's trouble at check-in or at the gate. It's no fun to carry a child a kilometer through an airport terminal!
- Realize that everything takes longer than you're used to. This is okay. It's part of traveling as a young family. Embrace it, don't stress. Try to see it as a learning experience for the parents too; look for things you can do better next time, but try not to get upset about this time, you can't change it anyway. Accept and embrace that you're committed to deal with whatever happens. It's not your regular business flight as an individual.