What would I need to really focus on or study if I decided to transition to an 18 series MOS from a noncombat/support MOS?

I honestly don’t think there is anything you can study that will help with selection. My advice would be to ensure you are as healthy, mentally and physically as possible going in. This as well as being used to carrying a 45lb plus water ruck for varying distances over varying terrain will help you be as prepared as possible.

The physical portion is always brought up, and yes it is demanding but it is partially just a means to break you down and see how you react to stressors. What do you do when you are put in difficult situations while sleep deprived, hungry and worn down.

To me it’s more of a mental assessment than a physical. Again the physical is to get you to a point where your mentality can be assessed. This is why I say to be as healthy mentally as possible going in. You don’t need to be worrying about things at home or outside stressors detracting from your focus.

The most important thing is to make it through the selection course. If you can make through that, you can make it through the rest of the training.

So, did you go to selection?

Never quit. Don't over train, stay away from supplements. Do your homework, make sure you can afford the time away for training and deployments. Never quit.

Land Nav, Land Nav and more land nav...biggest washout group on SFAS on my rotation was land nav....PT is a given, and with your current MOS, should afford you the time, nutrition and facilities to get in your best condition. Above all, no matter what, DONT QUIT!!!!

For selection, I would say running and rucking.
I am a small guy. I weight about 155 pounds going through, but was a runner and could ruck really well.
You will need the endurance. Guys my size, I believe, also tend to fair better as long as you can carry the weight there without getting hurt.
Others will have other opinions, but that is my advice.
Also, go with the ability to at least max the APFT, if not far exceed.
Otherwise, don't let the mindgame get to you. Most of the guys that were dropped or quit, it was because they let shit get to their heads. "I'm not gonna get selected." "I didn't perform well enough" "This sucks" etc etc. Just get through it. The first step is simply getting through.

Everybody says PT and rucking. While this is true you need to know land nav. This is a for sure way to get sent home if failed. DO NOT QUIT!!! Do your very best!! One task at a time.

Do you know any other languages?

I'm currently going 18X from an 11B although I'm a reservist so I'm also working on transitioning from the Reserves to active.