When a water heater breaks at 9pm on a Sunday I get an email saying it happened, it’s been fixed and it cost $1200 give or take.

More like a 101 of taxation: you had a reserve of losses -> it helps when you have profits.And a tax geek addendum:I also do not see a direct link to cost segregation benefits here.

He told me that without installing a sump pump system (at a cost of $12k), the foundation will continue to deteriorate, which could eventually lead to bowing basement walls—an issue that could cost upwards of $50k to fix.The inspector asked if the previous homeowner disclosed any water damage.

In a great and popular location with rising rents and upside on price with renovations but also that will cost in the short term to improve the property. 

You are correct in your assumption that it will impact how low they can go on the down payment, though, b/c commissions will need to be paid out of closing costs. 

DSCR could be a good option if you are refinancing quickly and if the value is higher than your cost basis.

Combined that can cost $50k+ which they may not want to pay nor their is the possibility they would not they pass the DD report.Nothing wrong with raising money in this fashion (FB or online ads), many do it and are great sponsors. 

Less Desirable Areas: Are there neighborhoods we should avoid or areas where BRRRR might be less effective?

In the future, I’ll factor in contractor costs more.

Since you're new, start by narrowing down a strategy—house hacking is a great way to get started with low upfront costs.