PERMANOVA in adonis2: correct use of factors

[AylenM]

Hi!
I'm really lost because I have read very different things of the same topic.
I have a continous variable of interest (X), but also factors that I think they can affect my results (for me the most interesting factor is Sampling site). So, I have made this formula for adonis2:
adonis2(X ~ SamplingSite + Year + Sex + Age + SampleType, data=mydata,method = "euclidean", permutations = 99999)
(Sampling site has 2 levels, Year has 4 categories, Sex has 2, Age has 2, Sample type has 2)

-Are these factors "fixed" in this way?
-Is this formula right? I know that changing order makes results to be different. Maybe because not all factors have exactly the same n by category? My total n is also <30

Any help/advice/suggestions would be greatly appreciated!!
Thank you in advance!