HI Alex
1. On the immigration form you must fill out the adress in Mauritius!
But I never must show a voucher, only the return flightticket
2.I stayed 11 x now in the north in holidays and I went to La Cocoteraie
http://cocoteraie.amltd.net
you can read about this accomodation on my website, under accomodation
www.mauritiustipps.de.vu
in the offsaison ,they have sometimes special rates.
Or call a taxi in advance and take a look arround for accomodation, it is no problem to get something.
But dont take a taxi from the airport, this people know, you must leave and so the prices are going high.
I can recommended a friend of me to you, you can read about him also on my site, under: Travel with the taxi.
His price from the airport to the north
is 800 MUR - 24 €
if you have more questions, mail to me
annth@web.de
greetings anne