good numbers before physically looking at properties + analyzing

[Jeffrey Grieshop]

I have been seeing this a lot, which is described in the title(with plans of buying and renting. they are usually 2 - 4 unit properties). A typical scenario may go like this: I come across one for sale and the owner states the income and something like "good cash flow" in the details. I dig up all the information I can find(property taxes, sewer/water, closing costs, purchase price, everything. I am using BP rental calculator). I input them. The numbers seem good. 

I usually use a typical 30-year loan at 4.75%, which my financing could likely be different(likely HELOC). So, I should definitely address this fact. Vacancy rate usually b/w 4-6%. I am assuming that is super ambitious come to think of it. Starting out, I would be ecstatic to have 19 out of 20 months rented out. I am usually using 4-7% on cap expenditures and repairs and maintenance, each. Many properties I have looked at are old, like around the century mark in age. Perhaps, I should be preparing for more maintenance and cap. expenditures, should I be setting these numbers a bit higher, to be conservant? I am asking for vacancy rates as well, should I set it higher(I always look into current lease terms if present)? I have often used property management at 10%. I usually have annual income growth, annual prop. value growth, and annual exp. growth all around 3-5% typically.

The purchase price, the repair, and the ARV I am usually being consistent with as well. Often times I am using a purchase price close to that or a bit below asking price. Sometimes, I will add a small repair cost (3 - 10% of the purchase price). Then, I usually keep the ARV right around the purchase cost. These variables, I believe, could be the big swingers. Some of the older properties I have looked at will need some updates. I won't really know until I get in and look, right?

I have not strayed far from these numbers and that is likely where I am going wrong and seeing a lot of consistency. The reality is, these properties will all likely differ quite a bit(the ones that I have run numbers on). 

I am asking for help in the process. Is my train of thought on the correct path? Will it take physically getting into the properties to put a lot more trust in the numbers? I mean, I think it goes without saying that is the case. I guess at this point, I am going to focus more on some of the variables and not go with "traditional" numbers. They can be a starting point but I have to really focus and project well when it comes to analyzing some of the numbers. Then, narrow them down, and start getting in them consistently and making offers. I think just typing some of these questions has already started to help paint a more vivid picture. I understand that the numbers should have a range too. Sure, property value growth may typically be 3% across the US and A but it still has a range, and the submarkets themselves will likely have an even wider range. So I have to think about "what ifs" and ceilings and basements too for the numbers. "OKaaaay."(Lil Jon) 

Any feedback would still be great. Any information pertaining to helping me accurately gauge some of the variables would be awesome. I have some people(who have skin in the game) who have offered to go through places with me, which is nice too.