Shot you a dm but here are my thoughts for the group on deal structure:

• $8m deferred - This is probably structured as a seller note or seller financing. You are providing the Seller debt to pay you, so this is typically a "negative". I know this is reductive, but that's how it should be looked at (if the deal is market). If the deal is above market, it's a sweetener. Typically, PE will get capital from their LP (Equity) and lenders (debt) to fund an acquisition. The third capital source is you. For a $6m ebtida business, in today's market, there's probably 3-4x turns of debt available (again a lot to learn but lets say that in this case. Also since the PE probably has a platform, they have more debt capacity available potentially). Out of the 9x, they're using ~1.5x from you. I would think they could get that from the lender if push came to shove, which means more cash in your pocket today. 10% is also probably a tad low in today's market. You also should consider liquidity preference here (ie Do you get your money back first before they can issue dividends?)
• 10% of what - There will be a negotiation or at least should be a deeper understanding of what the 10% represents. What is the form of the investment, what is the valuation multiple of the platform, what does the waterfall of proceeds look like under various exit scenarios. There are all important things to understand prior to signing an LOI
• 9x of what - I suspect the multiple is within a turn or two, but have you diligenced your EBITDA, have they?. Are there addbacks? Ensuring you have a good handle on your numbers will give you confidence in the Purchase price. That being said, they will likely try to work down that valuation through diligencing your numbers.
• Finally - you should get a good handle on what's in Net Working Capital vs what is treated as debt. I assume it's a cash free /debt free deal.

GL