Newbie investor here and would love some advice-TIA

[Keri Mallozzi]

I am currently looking into building a portfolio of condo units for retirement cash flow/passive income.  I currently have 3 making a few hundred a unit.  My question is I have good amount of money right now and can purchase 1 unit out right and make about $1300 on it monthly or should I spread it out and take out mortages and purchase 3 or 4 which will make me a few hundred each door? Trying to figure out the best way to build a quick portfolio that will give me 10-15k a month in 8-10 years.  I love reading all the forum posts and I see many different approaches. Any feedback and advice for this newbie would be greatly appreciated. Thank you so much!