Thanks for sharing Itzal,
I'm further down a similar path to you. Currently on resettlement leave after 8 years in the RN and I'm booked into Kingswood Training Services' MOD leavers course in April. I'm going to gain the new equivalents of CS30, 31, 38 & 39, plus stumpgrinder & chipper tickets. I've separately self funded my trailer towing licence too. A look on arbjobs shows these as a good start for gaining employment as a groundy with a view to becoming a second climber, in hopefully relatively short order. In all similar posts, the big recurring theme you will see is that we lack any experience. Hopefully a decent work ethic and receptiveness to training will mitigate that and accelerate the learning curve to catch up with the college kids.
I share your concerns regarding a saturated market, In the year since joining Arbtalk (the single most useful thing I have done to further my career change into this industry btw) there have been numerous ex MOD chaps appearing and asking the same questions as you and I have, and a search will show up many more before. I also seem to notice a lot more trucks towing chippers these days so I don't think the worry is unfounded.
The way I look at it is that I know where I want to be in 5, 10 & maybe 20 years and I've always got those in mind as my raison d'etre, particularly when dragging brash in the rain! I have a back up industry I'm looking at which can run alongside the Arb world if things are hard and I feel we service leavers have a few different talents that could put us ahead of the remainder of the 'qualified but inexperienced' hordes coming into the industry. So I'm quietly confident. Granted the path I hope to take to get there might be a little odd (I'm very fortunate in having zero responsibilities and healthy savings at present!) but to start with each decision will not be wholly reliant on having to pay the bills and more toward gaining the most experience. Its gonna be a massive pay cut initially, but that's not the point. As you say, its outside, free phys and hopefully within a positive and friendly industry.
Finally, I'm also inspired by some Arbtalk members/Arb industry professionals and their self respect. The threads about getting and pricing for work follow the same pattern and there always will be someone advocating the fact that they do a difficult job, well. Strive to be good at your job and have the confidence to charge a fair price. That (familiar?) attitude, encompassing honesty, integrity and professionalism, is one of the biggest drivers for me to get into tree work.
Hope my two penneth helps, Good Luck!