@Martin Snell you are on the right track to answer these questions. Financing is one of the most credit elements of understanding in order to prevent mistakes in SFR investing.
It is normal for a hard money lender (HML) to pay work in stages or "draws". Each hard money is a little different so some may only allow one draw and others may allow three and so forth. The basic concept here is that a contractor is not getting all the money up front for a job. The HML may allow 10% up front to help the contractor buy the materials but limiting the cash to the contractor protects you and the HML. It prevents the contractor from skipping town with all the cash (it happens). So this action is normal.
The other concept that I want you to be an expert in is the refinance rules for an investment property. If you are refinancing an investment property the two main tools that investors use are conventional lending or portfolio lending. Most HML won't even grant you a loan without a prequalification letter for conventional lending or portfolio lending if you are seeking to keep the property long term. A conventional loan can refinance your HML loan balance the day after the work is finished. A conventional loan will allow you to refinance 75% of the After Repair Value (ARV) of the home 1 day after the work is completed. But you can only refinance the loan balance or 75% ARV whichever is lower. If you do the renovation work yourself you may not be able to get that cash back for 6 months. Here's what I mean: Let's say you buy a home for $50,000. Renovation work is $30,000. ARV is $100,000. If you use the HML to buy the home and do the renovation work then your loan balance with be $80,000. When you refinance out of the HML the conventional loan can only refinance 75% ARV then your new loan amount will be $75,000 leaving $5,000 extra that you would need to bring to closing. Now gettig a $100k home for $80 is still a good deal but know that conventional is limited to 75% ARV....unless you are getting cash out.
So take this same scenario above, except this time the renovation work of $30,000 you pay for our of your own pocket. So your HML balance is $50,000. If you wanted to go above refinancing that $50k, meaning getting CASH OUT to pay back your renovation costs, then a conventional loan will make you wait 6 months. Once you start getting cash out the rules change. Cash out conventional loans still permit 75% ARV but you must wait 6 months to do it. So if the choice is between paying the costs on your own or using HML to do it, the HML route will allow you to leverage more of your money. BUT THERE IS ANOTHER OPTION.
Portfolio lending is another option. You mentioned that a conventional loan may not be the best for you right now and that's what portfolio lending is for. Portfolio lending is more flexible with qualifying you. There's always pros and cons to everything though. A portfolio loan may have a higher interest rate, it could be an adjustable rate, or it could be a 15 year loan, etc. So if that's the route for you then get all the terms for the loan so you know the full story before committing. Hope this helps!