Thinking of buying my first property - looking for some feedback!

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Hi - I am looking into my first property and was hoping to share the numbers and get some feedback in case I am overseeing something. 

Also, please feel free to give general opinions as far as what I should be on a lookout for, things to consider, anything as to avoid a rookie mistake. 

Asking Price: $494,000
Offer Price: $470,000

Down Payment: 20-25%

Monthly Income: $4000/Month

Property Tax: $7000 /Year

All Utilities paid by tenant.
Insurance: $1200/Year
Upkeep:$1000/Year
Snow Removal/Garbage/Misc: $1000/Year
Mortgage Expense: 30 year @3.75% ~$1800/month

Total Income: $48,000
Total Expense: $10,200 (Property Tax, Insurance, Snow Removal Etc) + $21,600 (Mortgage)

Net Income: $16,200

This is my first property that I am seriously looking at. I am not too familiar with mortgages and all so any help in that area would be greatly appreciated as well. 

Thanks!