Why not agus instead of is a?
'Is' (not being the copula and anything else) is an alternative to 'agus'
look at number 3 in the above link
Should this be pronounced mil YOON?
Here ye go: http://www.teanglann.ie/en/fuaim/milli%C3%BAn
1000001 marked wrong
I tried it too.
To say "one million one thousand and one", would you say "Milliún is míle is a haon"?