I have already shopped insurance, and the sellers are providing $5k towards prepaids/closing costs. 

My thoughts are to do an addendum (but not sure how to word it since she will have pre-paid her part until may) and let them figure out the security deposit between themselves at the end of the lease.

This is correct, but that .5% is IN ADDITION to all the other closing costs associated with a refinance (Title/Escrow Fees, prepaids, and depending on the bank, Underwriting / processor costs) - so in reality it can be a little more expensive to refinance with IRRRLs.

I have some of the required funds in a HYSA, but will most likely need to draw from another account and I'm curious which method is the most efficient in terms of taxes/capital gains, penalties, loan repayments, etc.Based on my previous transactions in the market, I estimate ~$45k cash to close: $20k for the down payment, $15k for closing costs and prepaids, and $10k of starting reserves.

There is a lot of confusion about what comprises closing costs and prepaids and understandably so.

Also remember 3.5% is your down payment, but you will also have closing costs and prepaids which might add to that number.#5. 

Using your throw-away prepaid credit card of course, to protect your credit, and complying with the contract terms -- I find teasers sometimes do indicate whether the subsequent seminar or product might be worth having your company purchase.

Financing provided through this program is only available for properties located in Michigan or Florida.Available Product Type: SOFR 7/6 ARM, SOFR 10/6 ARMLoan Amount: $766,550 MaximumLTV: Purchase and No Cash Out Refinance - Maximum 99%Prepayment Penalty: NoneLoan Assumption: NoneEligible Properties: 1-unit dwellings, attached and detached condominiums, PUDsEscrow: An escrow account must be established for property taxes, and flood insurance, if requiredUnderwritingNo Private Mortgage InsuranceOccupancy – Primary residencesMinimum Credit Score - 700DTI – Max 43% (UW/Mgmt exceptions up to 50% with minimum 3 documented compensating factors)Student Loans – If in deferment, no qualifying payment requiredDown payment of 1% must be borrower’s own funds, while closing costs and prepaids may be gift fundsAttached condominiums require a 10% down paymentEligible Borrowers – Protect and serve heroes are defined as employees of public or private education institutions, employees of medical and healthcare organizations, all first responders, and active or former military personnel.Servicing: Retained

on my commercial bank loans they generally  allow 20% of the loan pre paid in anyone year without penalty. but you do have to negotiate it .. and if you refi with the same lender early they waive it.. but again this is an up front negotiation at least with the banks I get commercial funding from

My down payment will be just as much as he still owes on the property, some small expenses, and maybe some prepaid taxes.