He said he charged $400 for his, is profiting well on it since he got his property for a third of market price some years before, and both he and his tenant are happy with it.

I paid for a lifetime membership and then still got charged. 

Is capital-gains charged for ALL properties or just for properties over x-value built after x-date?

You could also charge a damage deposit, though there are pros and cons to this.

I charge a completive market rate while providing a really good service. 

If you don't specify a charge in your listing, you can't collect it. 

Everything else is a total nightmare, with frequent failed connections and endless re-linking hassles.What’s even more frustrating is that, despite being a premium-paying customer, I’ve been chatting with Christopher from Stessa’s support team for over seven weeks, and he has genuinely tried to help.

You'll see some familiar names thrown around a lot: Stessa, Apartments.com, RentRedi, TenantCloud, Innago, RentManager, Avail, Rentec Direct, Doorloop, etc.I recommend you search for each app online and see what they offer, how much they charge, etc.

You have trusted contractors that are charging a fair price ? 

I am working with a RE-focused CPA this year who charges a flat fee of $2,500 and is very responsive so far.