If you think the value over time is very high, don't spend time optimizing the valuation now. Use the credibility of these advisor/angels to build the story of why you are going to be able to take advatanage of this large opportunity and spend more time optimizing the round following them. They also know there is likely to be additional dilution in the future, so you want them to have a meaningful enough chuck of the business to stay motivated and helpful. This is all an arguement for keeping the valuation low now and increasing it post angel investment.

Typically, establishing milestones and the credibility you can accomplish them is what enables an investment. People want to know what you are going to accomplish with their money. I find it's usefule to report your progress toward milestones and as well as any new information that would be useful in suggesting that new milestones may be more important than those on the current plan (pivots, new strategy pending, etc). I always assume you want your current investors to be future investors and that you should treat them the way you would wish to be treated in their shoes. On one hand its' seriously not OK to offer milesstones you have no intention of working to hit. On the otherhand, it's not OK to continue to work toward milestones you have learned will lead nowhere. Be forthcoming in what you want to achieve and put investors on notice that learning may change the milestones.

I'd need to understand a bit more about your business, but I suspect one answer is to work toward getting an accounts receivable-based credit line. Amazon is a good company that pays it's bills. Lenders will either loan against the Amazon receivables or buy them from you at a discount. This approach is expensive but if cash flow is your issue, worth exploring.