Should I go to Canada to get my H1b visa stamped for the first time?

Probably not. the Consular posts in Canada will generally not entertain a TCN on a first-impression basis.

Travel After Change-of-Status Approval with Future Start Date

You may abandon the change of status to H-1B as of October 1, 2014 by departing the US.

What will happen if there are errors on my old DS-160 document, but I have a new rectified document? (After taking the iv date)

What "issue?" You have not described what information is incorrect. Consult with an attorney of you are concerned about potential fraud issues.

Leaving the states after h1 status approved ? and come back on diff visa?

If you are afraid of leaving the country, do not leave the country.

You have to consult the visa bulletin when it opens up for FY 2015 each month to check where you stand in terms of visa availability.

How much financial support is required for NIW-EB2 (self petition)?

If you are deemed "likely to become a public charge" you could be found inadmissible to the US.

What if my j1 visa expires before my waiver is approved? (Edited)

It may affect your ability to change or adjust status, which is possibly the purpose for which you are seeking the waiver.

How long it takes to approve from uscis for change status F1 to F2b?

The beneficiary of an F-2B Petition may opt-out of a conversion to F-1 under the CSPA when the parent naturalizes in order to avoid additional...

Considerations for immigrating to the US, when I have student loans in default -? My boyfriend to apply for H1B work visa

A person who is "likely to become a public charge" is inadmissible to the US.

Can I use the 2007 H1B approved petition (approved never stamped) for cap exempt 2014 ?

If company B's petition would be cap-exempt, you do not need to be concerned with the 2007 petition.