HI @Quincy Davis welcome to BP and congrats on your first post. It sounds like you are off to a good start with your friend and are making some big plans. I can give you a little insight into a couple of your questions.
The loan program you choose will depend on a ton of different factors. Lenders are able to structure your loan in tons of ways so this ends up being a personal decision. One factor to consider is how hot the market is. In DFW FHA loans are not as strong as conventional loans for offers and realtors shy away from them. This is mostly due to a lack of education and psychology but it is definitely a factor at the moment.
Financing tends to be a very personal and case by case scenario. You should work with a lender who is familiar with investors and who can help you reach your goals. Things such as your down payment, closing costs and rate will greatly effect your ROI and your ability to purchase future properties. If you will be purchasing several within the next couple of years I would recommend sitting down with someone and creating a plan so you can maximize your leverage.
Your name will need to be on both purchases if you are financing the properties. There are exceptions to this but they are hard to obtain, I would plan on keeping your name on both properties until you are more established as an investor. Regarding your DTI it will make a difference when you purchased the property for some elements, ie whether you can include your rental income. But qualifying for investment properties is easier in some ways than a personal residence because you are allowed to use rental income if you meet the qualifications.
Personally i would recommend against having your partner be a tenant. But I do not know your relationship so it is hard to tell. There are advantages to having your partner live in the home since you could use an FHA loan.
You will need to consult a CPA for tax advice but it is not that hard to file taxes.
I hope that helps. They are big questions and without knowing the details it is hard, let me know if you have any other questions. Thx!