I take it by this that as 'curry' comes before 'carrot' in this example, that in Welsh, the adjective comes after the noun, like in Spanish?
No, that would be a different sentence using the verb 'to curry', which according to 'geiriadur academi' is 'cyrïo'
So 'I want curried carrots' would be 'Dw i eisiau moron wedi eu cyrïo'
The actual word is eisiau (a want). isio is just a phonetic spelling based on how eisiau is usually pronounced in north-west Wales, where it is often taught and written in that form.
In other parts of Wales it is often pronounced as ishe or isha, but generally spelled eisiau.
Stick with writing eisiau unless you have a strong reason not to.
I’m finding issues with it not accepting moyn (which is what I’ve learnt for ‘want’). I thought both were accepted by duolingo
I think eisiau is more popular but, like you, I was taught to use moyn and wish Duolingo could accept it.