Ask HN: How to convert US salary to a Canadian contractor salary? (remote)

Hey I'm having a bit of trouble settling on a dollar figure. The company I work for is a very early stage startup and they're not clear on details. They have no Canadian presence, so I will be working with them as a full-time contractor.

Current situation:

* Am a 24 year old Canadian.

* $25K made this year in self employed income.

* I do not have a registered business, I invoiced under my name.

My employer asked me the look into the following:

1) What is the equivalent Canadian salary for $80-100K base salary in the US PLUS benefits?

2) What $ amount does the company need to cover for my taxes as a self employed person? (I know it's something to do with CPP)

3) What is the total yearly amount they need to pay out including salary? 120k, 130k, 140k?

My personal questions:

1) Should I be registering a business ASAP or do I need to complete other stuff before I do?

2) My employer told me to fill out IRS forms W-8BEN (tax treaty document so I don't get double taxed) and W-7 (ITIN tax number). Are these documents necessary?.

I'm asking because none of this situation is black and white, for me, or for my employer so we're trying to work together to come up with a good number as they have no Canadian presence, so setting up payroll and benefits is not possible.

Thanks.