I agree wholeheartedly about DYI. We've had our refrigeration
repaired/redesigned/rebuilt by "experts" all over the world. That cost us a fortune and we had to correct much of their work. We switched to DYI and have been happy ever since. There's lots of advice on the internet
on how to build and repair 12V and engine-driven systems (we have both). R134a is readily available everywhere and works great.
If you do hire an "expert", make sure you get somebody who is actually familiar with boat systems. Also, try to arrange a payment schedule that doesn't involve the technition sitting around for hours evacuating and then recharging your system -- and charging
$100/hour for it!
I do have one peculiar bias -- toward flare connections instead of o-ring ones. The latter might actually be better, but flare connections can be made with a copper-tube cutting tool ($5), a flaring tool ($15?), and, of course, a nut ($.50?). Just remember, PUT THE NUT ON THE TUBE BEFORE YOU FLARE IT