I have my first actual house under contract.

There is a property in Modesto, Ca that we are interested in putting under contract with the purpose of flipping the property. 

There is a tenant in place, under a one year contract, paying $1050 per month. 

The seller and I have agreed to terms but I'm not sure how to write up the contract.

I wouldn't lie about anything but if for some reason they think they have tricked you they will clean thinking they will get their deposit back.Then you can quote your lease and explain they have broken it.I have had tenants suddenly start turning into lawyers and quoting some portion of they law that helps their case.It boils down to the contract they signed which is your lease.You could ask them to send the reference to law that states this for your attorney to review.

My thinking is that a buyer can backdoor me and go directly to the seller and offer more than my contract and less than my flyer price.

Recently got a home under contract with the plan to BRRRR, home has a renter but only a verbal agreement with the current owner. 

hi,We are currently Under contract on a four-square from 1920.

This is an off-market deal, and I will probably not go into contract without some inspection contingencies given my margin for error on my first deal. 

Also, if you go that route, don't forget you will need to add your marketing costs to each house you put under contract.