Plus after all this I still have about 50k in equity since they will only let you take out a certain percentage.

Just one percentage point off can cost you tens of thousands of dollars.Now you never said if the property is encumbered by nonmarket long term leases. 

So you'd have to try to purchase your properties with up to $50 per sqft of spread between your $ per sqft profit, and closing costs to properly plan your profit whether you're trying to flip/sell or hold and figure out how much equity you're creating.You can always get three bids to review how the contractors price their labor and their materials.You can call around to direct trimmers, plumbers, and other sub's to figure out what the general contractor is charging you since all the GC does is they work out a price with their Sub's and charge a fee or percentage on top of the sub's cost to make their fee.

NPN's generally trade at a percentage of UPB or collateral/property value, depending on if there's equity.

Just don't let your taxes and fees exceed some percentage of what the property may sell for at the master commissioner's sale.Tax liens that are not sold during the lottery sale can be purchased from the county clerk the day after the sale. 

I also have problems trying to figure out what parameters to use like, year built and percentage of equity.

You can deduct  the percentage land value from your calculation or if close (and in your favor) perhaps the counties land value as given.

I picked up the ones with a higher estimated market value with lower LTV percentages. 

What percentage should I give my business partner if he is only used for credit purposes.

My take is a certain percentage of Total capex should be treated as opex every year.