@Christian White
Talk to a lender, they will be able to help you create a plan, but this is my take on it.
If you did a cash out refinance at 75% LTV, is $225k, so you get a check for $50k because of closing costs, but your rate now is probably low and you'd lose that. I'd keep your existing low rate and do a HELOC, the rate will be higher than the refi rate, but I suspect the blended rate will be lower if you factor in keeping the original low interest mortgage in place and LTV should go higher on the HELOC, 80% you will get $70k because no closing costs. And the HELOC will be interest only payments during the draw period, use that as the down payment on the new property and then in a few years if rates go down and/or values go up look at doing cash out refinances on both properties.
Like I said though you need to talk to a lender, they have guidelines they have to follow and they will really help you create a plan.