I'm not 100% sure but profit- as well as solidarity tax should amount to something around 30% of a company's profit. If you add the dividend to the shareholders more or less € 30m of BVB's € 50m profit should have remained with the club. There are certain measures to decrease the profit tax like loss carryforwards but afaik BVB had few of those left as they decreased their debt considerably over the last decade.
Regarding their wage bill I believe you overestimate the influence of Lewandowski's increased salary on BVB's future personnel expenses. His replacement Adrian Ramos is supposed to earn € 2.8m according to BILD which is not a lot less than Lewy's € 4.5m. The remaining € 1.7m will be redistributed to Dong-Won Ji who arrives as a free-agent.
I agree with your assessment that the funds from the Uefa Champions League will give Borussia Dortmund room for proper net investments which is why € 30m seems like a realistic figure. That doesn't mean they have the money to sign players like Edin Dzeko though. His wage demands are still too high.
One thing is clear, BVB will not be able to compete with the Oligarch / Sheikh sponsored clubs abroad or the traditional giants like Real, United, Barca or Bayern when it comes to transfer fees and salaries. At least not in the next 10 years but they nevertheless grow as a business, they have to pursue their own road. The above linked report shows a record turnover of € 137m during the first half of the season due to new sponsorship deals (Turkish Airlines) and record-breaking merchandising sales. The more BVB can establish themselves in the elimination rounds of the UCL the more sponsors will be willing to invest into partnerships leading to further growth.
A stabilized turnover of € 300m would be a huge success for BVB and it's within their reach, even without increased ticket prices which could lead to disturbances within the club.
My point about Lewandowski's increased salary was in reference to your well-grounded claim that Dortmund has shown 50% less profit in the first half of this season compared to last season due to bump-pay for their key players that resigned. I just highlighted Lewandowski's salary as an example. The likes of Subotic, Pisczek and the rest have also likely received a significant pay-rise when they signed their new contracts, and that is surely the reason that Dortmunds profits have gone down by 50%. As you mentioned, the report shows a record turnover.
I agree that they cannot compete for highly-paid players like Dzeko (who's not very good anyways). However, they could and should go after the likes of Firmino to boost their ranks and replace Lewandowski. They also need a bigger squad. The injuries derailed their season because of a lack of cover in key areas.
With some smart moves, Dortmund could establish itself as one of Europe's superpowers. They will never have the financial muscle of the sheikh-backed clubs, but they play in a competitive market, have a massive stadium, and dedicated support.
