Is mise X is a very "Irish" thing to do. In Scottish Gaelic it sounds at best antiquated, at worst plain wrong.
With the exception of name-giving.
Is mise Màiri is totally ok in Gàidhlig.
However, most people on here seem to use the 'e' form, and infact one person asked why i use 'i'. Is it just that 'e' is the accepted form even though both are correct, or is there other rules governing there use. (e.g. When also referencing a gender in the same sentence i.e. 'it belongs to her')?
What Màiri75 said but let me add a note to it - it also depends of how formal the situation is. In colloquial Gaelic, most native speakers default everything to
e unless there's biological gender involved (or certain fixed items). So for example in really formal Gàidhlig this would be ok:
Tha coinneal dhearg aig an uinneig. Cheannaich mi i [i.e. a' choinneal] ann am Boots.
Seo Màiri. Tha i ag obair aig a' Chomhairle.
But colloquially you're much more likely to hear
Tha coinneal dhearg aig an uinneag. Cheannaich mi e [i.e. a' choinneal] ann am Boots.
Seo Màiri. Tha i ag obair aig a' Chomhairle.
The "fixed items" which still invoke
i across the board are: language names, the weather, boats... off the top of my head, there might be a few others.
), because the gender is in this moment also important if you exchange "the car" by "it". Although it is not obvious in the very first moment. 
