Typically Conventional will end 42% of DTI and FHA can get up to 51% DTI (and based on your credit score I think you should stretch to that 51%) Just a few things to start thinking about as you are working through the process. 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

I have broken down 4 key benefits to a retirement account: 1) Compounding interest in the absence of taxation (particularly with a Roth IRA) 2) Ability to self-direct into alternative assets, like real estate, private real estate partnerships/syndications, crypto, gold & silver and other alternative investments. 3) Credit protection (see state specific laws), but generally inherent protections. 4) Upon death, if setup properly, probate avoidance 

Do you have an idea of the total tax credits?

Examples could include:Partnering with other investors to share risk.Using seller financing or lease options.Leveraging creative rehab techniques to save on costs.Negotiating with contractors in a unique way to reduce expenses.I’d love to hear any stories, tips, or approaches that helped you pull off a deal others might have instantly passed on.

I have a lot of bank accounts and credit cards and it seems impossible to keep track of everything.

Take a look at the overall picture, i.e. credit score, debts etc.. to make a decision.

Some lenders do have minimum credit scores to access these loan types, but it is the exact same qualifications for income and assets as non renovation loans. 

I have no debt aside from the properties and regular monthly credit card debt.

Have about 50k I would invest (access to more), with excellent credit and good income too, from my full time job.