I'm sure securing a job wouldn't be an issue in the NHS, there are always reports about how many vacancies they need to fill for skilled people like nurses. That being said the hospitals are few and far between so you may need to look more at community nursing provision which could mean unstable hours. Worth having a look at the areas you really like and how close the nearest hospitals are. The NHS in Wales is performing really poorly though so expect it to be straight in and full on from day 1.
Remember, whilst you're happy driving the roads up there are largely rural and twisty so slower average speeds, especially during the tourist season so factor that into any commute that you're happy to build in.
Looks like you're favouring the Gwynydd area which is largely considered to be one of the Welsh speaking heartlands. There probably are one or two English medium schools but definitely do your research on where they are and how likely they are to have spaces.
If your children enter Welsh medium then all of their lessons except for English will be in Welsh. Primary school that's pretty straight forward but secondary school can be tricky - all math and science terms will be in Welsh for example and learning modern languages like French/German/Spanish are done via Welsh. In secondary school literally the only lesson taught in English, is English language/literature. I'm not a Welsh speaker and my children attend Welsh medium, they are learning sponges and take it in so well - but it's not easy as a parent when you try to support their at home learning activities.
Really not sure about more specific local things though sorry as we're in South Wales (have visited the North a lot). I wouldn't expect SENCO provision to be excellent, anecdotally everyone I know local to me who needs extra support for their children has to fight tooth and nail for it.
Might be worth checking local news websites from now on to get a measure of the kind of things happening in the areas you're interested in and if possible local Facebook groups. If the most interesting thing in the local FB groups are missing pets and complaints about dog mess then you're probably heading for a decent enough area.
Best of luck, it's a gorgeous part of the world and I've seriously considered moving up there myself...it's just the 4 hour drive to see my mother that stops me!