Take the levers one at a time, because three of the four are narrower than they look.
Seller credit is the workable one, with a ceiling. Conventional financing limits what interested parties may contribute toward the buyer's costs, and the allowance on an investment property is materially tighter than on an owner-occupied purchase. On a 250k purchase you may find the cap sits at or near your 5,000 before you've applied a dollar to prepaids or title. Get the number from your lender in writing for your specific program and occupancy type, since these limits get revised and vary by product. Also confirm with them how they're treating buyer-broker compensation paid by the seller, because guidance on whether it counts against the contribution cap has been moving since the settlement rules took effect.
Financing the fee into the loan isn't a thing. The commission is a closing cost, so the only way it ends up in the loan balance is indirectly, by raising the price and asking for a credit back. That works until the appraisal doesn't support the higher number, and on a 250k investment purchase you're often near the edge of the comps already.
Rebates from the agent are permitted in most states and restricted or prohibited in some, so whether that's available depends entirely on where the property is. Ask the agent, and ask your lender too, since a rebate applied at closing shows on the settlement statement and the lender has to approve it.
Basis treatment is a live question and your accountant answers it.
The lever you haven't mentioned is the agreement itself. 2.5% on a 250k house is thin work for an agent, which is exactly why flat fees are easier to get at your price point than at 700k. A fixed 4,000 with a per-property compensation addendum removes the gap risk you're describing, and if you buy more than one property a year, say so before you sign.
