Legal presence in USA after I485 was withdrawn

Yes you can withdraw and remain in F1 status and apply for your OPT later on. All the best,

Yes you may do so if you are currently in a legal status. I suggest getting help from an attorney. All the best.

Is it necessary to change to business visa waiver (WB) and how can I do that? Is it possible to do it if I go to Canada?

Tourist visas are given not only for pleasure purposes but also for business purposes so you may go ahead and do what you wish without changing...

Can I provide my wife's income with my income as a joint income for i-134?

Yes that is totally normal. All the best.

Not a good idea, you are not supposed to work at all in tourist visa. And when you read your question it says "Pro bono WORK". So please stay away...

What are my chances of gaining a US visa and what is the best way to rectify my mistake if i am in fact ineligible for VWP?

I agree, please consider talking to an immigration attorney. Avvo now offers fixed cost legal services make use of them. All the best.

It is not a good idea, you might possibly get a bar from entering the country if you get caught. All the best.

If I get a job-offer from an US employer located in mainland, can I work for them and move to mainland to work there?

1. You may be able to move, but we need more information to confirm. 2. The company will decide that, they can do it in the first month or they...

Does a Mexican TN Holder with a new Extension I-94 need to get a visa to reenter the US?

If your I-94 is still valid for more than 6 months when you return you might be able to enter with it. All the best.

Could getting married right before applying for naturalization raise a red flag or slow down the process?

It might be a good idea to marry her after you become a US citizen. Because depending on which country she is from the green card process will take...