My son and I plan on buying our first investment property; either a duplex or triplex.

If they are month to month, just tell them you are planning on remodeling the place and need it vacant.      

I am trying  to purchase a multifamily house , outside of the city where i live it wis about 150  miles from my location ,  how do i figure out the demographics of the area and also the medium income around the area where i am planning to purchase . do i need to look for any big stores/shopping malls or any govt offices around the area to see if the place would be ideal for purchasing the property for renting it .

You likely have to live there longer and/or plan to use it as a rental property (assuming the revenue is high enough) because you're starting at zero equity.  

I assume you have the foundation permit/plan and can provide that to them to bid, so you just need to send it over and have them provide SOW and pricing. 

Without a full summary of the STR tax loophole for high W-2 wage earners, here is a link to the best explanation and summary I've come across and helped me digest the value of the benefit: HERE In short, the bonus depreciation rate was 100% in 2022, 80% in 2023 and is planned to be phased out to 60% this year. 

remember your first home is not your forever home, it's your first rental so it doesn't need to be everything you want.look for homes where the bones are good, but cosmetically needs love. don't by pre 1960 if you can help it. you'll end up just having to replace all the guts like plumbing and electrical at some point. it's inevitable. look in areas where the path of growth is headed, but might not be currently. think 5 years out. look for resources like your local chamber of commerce to see what businesses are coming in and where. your city planning office should also be on your call list as they can help show where most permits are being pulled for development. follow the money. go to local investing meetups. crowdsource local knowledge and form meaningful relationships. those who've gone before you typically will help out and help you avoid the mistakes they've already made. onward.

Just make sure you are talking with an actual investor when you take advice not someone that is "planning on" investing. 

That would increase the desirability.What do you exactly mean by approved plans?

If you are planning to hand off, I wouldn't worry about systems and processes; they will have their own they utilize.