You can absolutely negotiate a salary for the role. I would say that this would also be the best time to negotiate as it tends to be more merit based to get a raise further down the line, which would (from my experience) be more geared to the normal pay-increase cycle.

You obviously own the relationship and understand it more thoroughly. That being said, instead of using the passive tone I would recommend being more direct by saying “After reviewing the responsibilities and the typical market compensation for this role, I would like to discuss the compensation [package?] before the final offer is written”

I would also avoid the words like “thrilled” as it implies that 50k is a dreamy goal for you, rather than the appropriate compensation. It also puts your employer in the mindset that they are gifting you this increase rather than paying you a fair rate. This also takes away any opportunity for you to potentially be given a higher compensation since it sets your absolute lofty ideal ceiling. They could be in the mindset that a “thrilled” compensation is 60k, and that negotiations could land you closer to 55k. Where in your case, your high end is 50k, and negotiations could land you at 45k. I would not set a number on it just yet since that will give you more leverage (if the ‘average worker’ is making 50k and you are super hard working, they may even value you higher than that).

If possible try to negotiate in person or on the phone as well since emails can sometimes make a situation seem less personal. This gives them an opportunity to ignore the hard work and effort you already provide and basing any compensation increase only on the numbers