Do not sign any exclusive agreements and ask for comps when they agree to submit your offer.Sooner or later you'll find who you want to work with.

For example,If I put a house under contract, should I seek to get an exclusive right to market the house?

You being the buyer is important for the purpose of you taking the IRS section 121 exclusion on capital gains should you ever sell.

Once this is accomplished then it becomes sec 121 property and the same primary residence tax free exclusion is available to you on this property as with any property with two additional requirements.  

Not sure how that is handled, if it's still considered your primary for the 121 primary exclusion, but I don't think so.

Can the house be put under non-exclusive contract for the wholesale on a 30-day buffer with the option giving the homeowner to still work their other options?

For regulatory purposes (i.e. accredited investor) there are some exclusions for instance your primary residence doesn't count. 

For example, if you live in the house for 2 out of the 5 years prior to selling, you may be eligible for the exclusion of capital gains tax up to a certain limit for single or married filing jointly taxpayers.

When you sell, the gain associated with your 75% will be tax free from the 121 primary exclusion. 

I'd have to sell my exclusive membership to the club in Laguna Beach and move (except I don't belong to an exclusive club, but your get the sentiment.)