Buying properties through an LLC can provide some liability protection and may help to separate your personal assets from your business assets. However, it does not typically affect your debt-to-income (DTI) ratio. Your DTI ratio is calculated based on your personal income and debt, regardless of whether you own property through an LLC or personally.
As for how it will impact you when you want to buy a primary residence as a first time home owner with a 3.5% down FHA loan, it will depend on how you are using the LLC and the property. Rental income from properties owned by an LLC can be used to qualify for a mortgage, but you may need to provide additional documentation, such as tax returns and financial statements for the LLC. Additionally, if you are using the LLC to purchase and rent out multiple properties, it may be considered a business and your lender may consider your income from the LLC as business income, which can be treated differently by lender during the loan underwriting process. It's always best to consult with a mortgage professional to see how owning properties through an LLC will affect your ability to qualify for a mortgage.