Robertorolfo - welcome to bike racing, and to the forum. Congratulations on your first race - sounds like it went really well. Your equipment is just fine to start racing - don't worry about it or what others think. You are right that it isn't holding you back at this stage. Your helmet is likely just fine, but you should check that it is approved for bike racing. Requirements and standards for helmets differ by use and even though it might protect you just fine, it might not be approved by cycling.
Regarding all the other questions - It is easier to move up on the leeward side of the pack - nice job figuring this out on your own. Use that knowledge to your advantage. Sometimes in any bike race, and likely more so in a Cat 5 race, there are lulls where the rider on front doesn't want to work in the wind and slows to try to get other riders to do some work. This also is a time you can use to move up without working hard. And regarding being slightly off the front after you led into the last lap, that also is common. You are right, the pack probably thought you wouldn't survive out there and one strategy is just to let up, get back in the pack and do your best in the sprint. But don't be afraid to get aero and give it your all in that position. You will likely get caught and be tired for the sprint, but sometimes the pack will look at each other hoping someone else will bring you back for long enough for you to stay away to the finish. More than a few races have been won that way.
Keep at it and have fun.