The biggest lesson I learned was once you determine the market you want to invest you need to build your Team.

TENANT:  Oh, I wanted to make it a 2-bedroom apartment.ME:  --Biggest facepalm ever-- You need to contact us before you do any sort of modifications to your apartment.TENANT:  Oh, I didn't know that.ME: My manager will contact you on Monday.Needless to say, she probably won't be staying very long...

My biggest complaints are similar to yours:1. 5-7 days or more from the time the tenant pays the rent until the cash hits my account. 

Your biggest risk is kids commandeering the thing while mom and dad are in the hot tub,and running over and killing someone(s).  

That's your biggest hurdle.2) Of that remaining 100, on 95 of them the appraisal is going to find some reason to kill it.

When dealing with legal matters, the biggest mistake folks make is not listening to the attorney.It sounds like you’re out of town. 

I think the biggest factor to determine which route to take is how much money do you have to start with and how much do you want your investments to be worth over some set period of time (i.e. 10 years, 20 years, etc).If you're starting with 100k and getting 10 to 12% return, you're making 10k to 12k a year?

I think the biggest obstacle is getting a lender that can work with you.

My biggest problem these days are more (in some cases MANY more) people living in the apartment than are on the lease. 

What has been the biggest benefit and/or the greatest challenge?