I'm going to give you a generic /r/realestate answer: You and your friend need to hire a CPA to best answer this question.
If it is a FSBO you would probably be better off without a Realtor. Make sure you have an attorney if you don't have a Broker and the seller will have to do the same. A benefit of having a Realtor would be if you plan on continuing to invest in property for income purposes. That way the broker could keep an eye out for additional properties you may be interested in. This is dependent on your long term goals.
You will have costs for appraisals, inspection, loan origination/lender fees. In my area (Colorado) we generally see 1-2% of the purchase price for closing and borrowing costs.
The big cost you don't mention will be vacancy rates of the property. If your current tenants move out how long (read: how much $$) will it take you to advertise and get the property occupied? Also: taxes, insurance, bookkeeping, CPA, yard maintenance, background checks for tenants, tenant damage. That's all I can come up with for now.
This question is tough to answer without knowing your 'division of labor' with the partnership. My thought is to hire out everything you do and split costs, as well as gains, 50/50. If you/your partner are doing more of the work try to find a fair rate to pay that person and they can submit an invoice to the LLC for payment.
This is a must! Talk to a CPA for more information on the reasons why and what your best avenue for protection may be.
Another hard question to answer. You could possibly have tenants that pay on time, take care of the property, and will be there for a long time making your job very easy. On the other hand you may have tenants that pay late, trash the home, call you at all hours, and have a turnover every 6 months. This is one of the risks with becoming a landlord. Take a look at your neighborhood and keep an eye on rental listings to get a feel for the rental market in your area. Also, do background checks on your prospects, the costs are worth it!
I hope this helps and you can let me know if you have additional questions.