Whatever thickness you get, try to get it with padding so you dont have that extra cost in material and labor

For example if I do a fha loan and my down payment is around 5k, how much extra should I have saved for this ?

It affects all their income not just the marginal return a few extra units can bring.Anyway thank you all, this has reassured me of my strategy.

Refi will cost you $$$ and you may need the cash to continue improving the property or paying more taxes if the reappraisal increases your tax base Also you may need the extra cash if a tenant can't pay rent. 

On my end - I've heard that some of the easiest (and potentially cheapest) tricks could be:- applying a fresh coat of paint on the exterior / interior living room spaces of the home- refurnishing doors / door knobs - updating the lighting of bathrooms or kitchen area light fixtures- bathroom refurbishment- curb appeal / clearing out excess weeds/trees/shrubbery.I've also heard of situations where the home owner would either offer to build, or provide a backyard shed for the tenant as additional storage space, charging an extra $100-$150 per month if the tenant wanted to use it. 

I want to open a side business due to the extra income I am already making.

On top of this I got charged an extra 10% on the invoice price  Should I be worried about this and start interviewing new property managers or am I over thinking things? 

Hi Pedro,I would recommend looking into a property that has a detached garage or extra space in the lot to add/convert an ADU, that's the safest way to cashflow.

So if you can cut that down by $1000/month, it's like making an extra $1000/month.

I'm probably just going to keep the communication channels as open as I can, and encourage them to send whatever they can as they have some extra money.