I am currently searching for my first property, but I am finding it a challenge to make it happen within 70% of the ARV(ARV found using the low end of comps).

What about maintenance costs?

The problem is that most agents don't want to run around and show you 30-40+ houses, put in a bunch of low offers just to find out you can't qualify down the road (not saying you can't qualify, but they don't know that)..

Using that rate may be considered alright or it may be a little low and raise a red flag somewhere.

Am I being too conservative at 10%capex 10%repair&maintenance 10%property management and 10%vacancy.

No management company is an expert with low end renters.

It's a mix of 3 bed (8) and 1-2 bed (7) units, came 75% occupied and with a lot of deferred maintenance.

If that's the case,  you have locked in a low property tax base, and a fantastic (high paying, easy to find, easy to manage, etc.) tenant profile, which I would not want to loose.

Anywhere you have low lying areas close to water you're going to have an added carrying cost for flood insurance (unless 100% equity).  

The repair costs seem low for the Midwest