Just after, the book talks about improving the property so rent brings in more money per month/year, which increases Gross Rent Multiple. 

I agree, improve it now as if you were planning on selling.

I myself am not. and most flippers are not GC's  so all of us non GC's need the developers license.. now there is no test just pay the fee. you must have proof of insurance and a 50k bond.. the bond and insurance for those that have little to no money or bad credit can be a stumbling block.

My credit is great and I can put up 25%.

Eventually, if you are trying to get hard money or a credit line, this becomes much more of a factor.

Try your local banks and credit unions.

After you've done some strategic improvements and built the tenant stability, you can sell the property and roll the equity into another with no out-of-pocket down payment.

We will be raising rents to market value and improving the units to a more modern look.

@Anthony JankeFinding something that would reduce what you are paying in rent would be an improvement but I would encourage you to try to find something that would at least cover your expenses. 

Some people recover, but cutting your body to "improve" your looks?