You need to see his IRS tax return on these properties to verify the profit and loss. Need to check with tax assessors office for property taxes, tax rate and payment schedule and if there are any delinquent taxes to be paid. You need to see the insurance policies, are they up to date, can you renew with thier company on same terms or will the premiums go up when you purchase. Or do you have to get your own from your own company. Check with utility companies to get actual costs, are they up to date and are they on a budget plan. Are there any flood concerns? If so do they have flood insurance and will the premiums go up with a new owner? Also need to have the rent rolls and verified monthly rents, who is paying, to whom do they pay, date of last payments, are there any arrears for rent payments and are there any current litigation's going on at present for nonpayments. Need to have your attorney or title company do title search on all these properties of course for proper title transfers on all properties and lien search to determine if there are any current liens on the property.
Have you viewed each unit to determine repairs and Cap. EX. for near future? Have you looked into a professional management company for rates and terms? Or do they have one employed, and if so what are thier terms and can you continue with them?
Have you looked into rental rates for the area, are his low, is there room for increases as soon as you take over?
And most important is what will it cost you at your first day of ownership and are you prepared for this? Will you have to do evictions that day? Who will be collecting the first months rents? Do you have bank accounts set up starting on your first day, rent deposits, security deposits, maintenance budget, utility payments, etc...