@Dylan Fellows To estimate the rent, you really should check multiple sources and try to get the best comps/data you can. I've compiled many of the top sources available in this blog article here: How to Determine Fair Market Rent
It also gives you an explanation, and the pros/cons, of each one. So hopefully that'll be of some help to you.
As for how to estimate repairs, that can be a little tricky as there is no one specific formula. Many people will just use a % of the purchase price. However, you have to ask yourself...if you have to replace an HVAC unit, is the HVAC company going to charge you 75% less because you bought the house for $100k instead of $400K? The point is, repairs are not based on the cost of the house, so why should we budget for them that way?
Plus, there are so many other factors that can affect how much we spend on repairs. Things like the age of the house, condition of the components of the house, class/quality of the tenants and how hard they are on the property, how long existing repairs are allowed to go unrepaired (e.g. if a roof leak were to not be repaired in a timely manner it could end up causing additional ceiling, wall, and/or flooring damage that maybe didn't have to happen), etc.
So it's really all just a guessing game. I have 70+ year old properties that have cost me nothing in repairs each year, and other properties much newer than that which have cost me thousands in repairs. Ultimately, it's better to set more aside than you think you'll need, and if you don't end up needing it, great. But at least you have it ready/available in case you do.