I budget 10% for vacancy and 20% for maintenance/capital improvements.  

Don't forget to account for vacancy, repairs, capital expenditures, property management (even if you self-manage, there will likely come a time when you don't want to), and water/sewer (if you pay for them). 

There many things you need to know ideally before you make an offer.Your first thing and not necessarily be the most important is the first impression when you drive like the building(s) and the landscaping, is it's location good for your tenants, the mix of the floor plans, can you add any value, Make sure when looking at the income and expense records that you looking at actual financial statements.Are there any nearby schools and are there there any nearby amenities and what type of the parking is available to the tenants, how any nearby apartment locations and what, if any, are they doing to attract prospects, look at all units and do not let the current owner trying to get you  not to do that, how does the current rental rates being collected near the market average, does it need any capital repairs or rehab right away,does it have a positive cash flow now, is it being properly managed by property management, and is there any nearby retail development and do its match your target market.

Can I pay capital gain on this $ 500 k or I still have to pay regular income tax on it?

You can sell with a monetized installment sale, which results in 30 year deferral of capital gains tax, and provides you with 93.5% of your net sales proceeds in cash.

I should have approximately 50k in cash capital in the next 1-2 months.

Make sure to include monthly expenses for lawn care / snow removal, insurances, any utilities you'll pay, repairs/maintenance, capital expenditures, vacancies, taxes, etc.

I know a lot of investors who love this market and make money, but they have a massive hands on management team, and large contractor crew of employees, and its still difficult with massive capital reserves.

I have been in the construction industry for a long time and I see many investors struggling with different aspects of investing when it comes to repairs and capital expenditures.

While cashflow is my ultimate goal, I may need to do a few flips in order to restore capital and pay down debt (BRRR likely won't work on this first property, at least not for another year+)@David Clinton III Next time I'm in town I'd love to pick your brain and see what value I can drive to your portfolio.