A storefront under apartments is said to be harder to finance, and it is worth being precise about how

The financing issue is real and it is mostly about the percentage. Different lenders draw the line in different places for how much commercial income or commercial floor area they will tolerate before the loan moves from a residential product to a commercial one, and the line shifts over time, so the only way to know is to ask three of them for it in writing before falling for a building. What deserves more weight is that the term length matters more than the rate. A five year term with a balloon means a hard date where the owner has to refinance or sell, and if the ground floor is empty that month the options narrow. A ten year term buys two chances to lease the bay before anyone makes you prove anything. Two years deciding on a first one is nothing to regret. The time that tends to get wasted is the months spent on buildings before a single lender has been asked what they would actually lend on.

A first purchase is usually better served by the four apartments on their own. The diversification argument for mixed use holds up well enough. The difficulty is that commercial leasing is a separate skill with its own vocabulary, and a first time owner ends up negotiating that first lease from a position of not knowing what is normal in the market. If the mixed use building is the one you buy, buy it with the bay already leased to a tenant with years left, so your first commercial lease negotiation happens as a renewal with someone already in place rather than starting cold with a dark bay and a mortgage.

One thing nobody has said yet is to check what the zoning actually requires of that ground floor. In a lot of walkable older neighborhoods those buildings sit in a district where the ground floor is required to stay commercial, so if the bay goes dark for two years you cannot simply make it a fifth apartment. Some jurisdictions have loosened that and some have not, and it is a question for the planning counter rather than the broker. That cuts both ways for your decision, quill. It is a constraint on your exits. It is also part of why the retail down there has value, because the supply of ground floor retail in that district is capped by the same rule.