When is rwy used in conjunction with eisiau? Rosie
The two are completely independent.
Rwy is an alternative form of Dw i (I am). It is quite often used in written Welsh and you will sometimes hear it spoken, too.
Does 'Dw i moyn tost' make sense?
You will hear that is casual spoken Welsh, but it should be Dw i'n moyn ...
The pattern with the noun eisiau with no linking 'n/yn is an exceptional one in Welsh.
moyn is a verb-noun, so it should be used with the linking 'n/yn.