I have a plan. Help me improve/identify flaws.

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Okay so let me give a quick background on myself. I had a windfall of money in the past and after paying off a bunch of school loans I am currently left with about 330k.  I currently own a two family home that cash flows around $850 per month.  I have a full-time job, a wife, and a daughter.  My long term goal is to expand my portfolio and eventually own around 30-40 rental units.  My current dilemma is figuring out my next move.

My current plan is to find a two family home that is move in ready (my job/family does not leave me much time to rehab). I have come across a few potential properties for sale in my desired area that range from around 150-170k. I plan to make a cash offer under the asking price on one of these properties or a future property I come across. Once I acquire the property, I will own it outright. I estimate I should cash flow around $1,500-1,600 per month. I then plan to sit on it for a year and save as much of that income as possible. I will then take out a HELOC and use that money plus the money I saved up to purchase my next property and repeat the process. If I continue to buy a new two family home each year I should have 30 units in about 15 years. I realize this is pretty much the BRRRR method (minus the rehab part).

My questions are: Are there are any flaws in my plan? Can my plan be improved in any way? Is this plan right for me with my current situation? Is this the best way to leverage my 330K? What potential problems may I run into? Will I eventually have trouble getting a HELOC because of my increasing debt? Any advice is greatly appreciated! Thanks in advance, you guys are awesome!