(To the Mods/Admins/and other members : I know I haven't posted on this site in a long time, I've been in and out of various schools in various places so I apologize for my lack of presence)
To the OP: as someone who recently (I won't say how long ago) came into a certain USMC community, I will tell you a few things that may help in your decision...One thing I always say is Maturity, maturity plays a huge factor in your success, or lack thereof, in a selection school such as A&S, BUD/S,BRC, etc. You can be a PT god and still fall short of your goal if you aren't mature enough to face adversity. Everybody faces adversity at some point during a Selection type school you will be tested, you can either persevere or you can go home. Just because you're 18 doesn't mean you have an excuse to not be mature enough.
So in reading your original posts and seeing your goals, it seems like you want to be a "badass operator", it's ok. However there is a big difference between WANTING to be that guy, and NEEDING to be that guy. I don't quite gather from your post that you NEED to be what you say, I could be wrong. I won't fool you here and say I was never afraid of failing my schooling, I worried everyday constantly, but I believe that lead to my successes thus far, it kept me going 100% all the time. However, I didn't let percentages and numbers of attrition rates prevent me from pursuing my dream in the first place. It does not matter if the failure rate is 99% or 1% there's always a chance at success , if it is what you need, go for it and then fight tooth and nail to succeed. I promise you with whatever route you decide, it will take Blood, Sweat, and Tears.
You do have somewhat of a" backup plan" in case you don't get selected at A&S for MARSOC or earning the Trident at BUD/S or whatever the hell you decide, however I think you should do a bit more research on your own about that plan and form something more legitimate. You wont find that answer on here, maybe some tips, but that's about it. You will find a ton of great information and resources to get you started, but YOU have to do the research.
Whatever you decide for a path for your future I wish you nothing but success, remember your fate is not predetermined by statistics of attrition rates, it is determined by the heart and soul you are willing to put into it.