I'm closing on my first investment property, a 4-unit mixed-use in Yonkers (1 grocery/deli/corner store and 3 residential).

You need a signed lease and security deposit, and the lease starts when they take possession (which is the day you give them keys, whether to move in, prepare for him, or just store a box.More important to the lease, you need to make sure that you clarify terms about altering the property, and having it restored upon him move out. 

They ended up taking over 3 times as long as promised and when you call the store they say it's the contractor not them. 

Since you are starting with a basically clean slate, don't make the mistake of starting out with store cards or cards that are marketed to those with poor credit.

Especially the store Organica that’s next to shop rite!

If you go to sell it with them in there you'll loose 10% off the value of the home in transaction costs not to mention how much you loose off the value of the home by selling it with tenants inside of it when it's clearly not a house that is geared towards investment.So let's do the numbers on this.Let's say value of home is $125k.You'll spend $12,500 in transaction costs (Realtor commission, Title cost etc)You'll loose another $20k selling it as a beat down rental (No 10 year rental comes with fresh carpet & updated kitchens guys)So right there you're in the hole $32,500. 

Get a weekend job at the hardware store. 

And it's a $500 mistake gone, instead of impulsively buying another house that he may not be fit for.You're looking at it like it's a candy store. 

The lease has 2.5 years left, but the tenant has closed this store and offered me a lump sum (1-year rent amount) to get out of the lease now.

You will be done with the first room before the other person even picked out a color and had it mixed at the store....Plus, use the good stuff (whatever brand that may be for you) and you may get out of some shorter tenancies or one with lower wear and tear tenants with just a touch up and by washing walls.