I am currently running a Lund E85 tune with very basic mods. With an off road x-pipe, resonator deletes, Roush axle back mufflers, and a JLT intake (along with the 47lb injectors of course) I made 416rwhp/393rwtq. Now that we're on the summer blend, which was tested at E90 at my usual station last week, I'm probably working with 420/397...ish.
A tester isn't mandatory, but very helpful. I check the local racing forum since they have guys going around and checking our 5-6 stations monthly. We have 2 or 3 that are to be avoided at all costs because they run shtty blends all year 'round. Also worth noting that in the winter (October here in KS), if you still want to run E85, most blends will be around E70 because cars have a harder time starting in colder weather.
There is a company (VMP) that will give you an E85 tune with stock injectors for $150, and since you're stock as far as the engine is concerned, you might be alright. The problem comes when modifying the engine because it will put your stock injectors very close to being maxed out. To me, it's worth it to do it right, especially since you plan on engine mods in the future, and get the 47lb. I paid $175 for mine used, new they run closer to $300.
As far as which tuner, most will say AED or Lund. AED's customer service can be hit or miss and Shaun will ONLY tune the FRPP 47lb injectors and will not refund you if he discovers they are incorrect after the process has started, then will charge you again once you get the correct ones. Lund's customer service is, hands down, the best I've ever had. Email responses within literally MINUTES during business hours. You will have to be "remote tuned" for either of these companies and it's worth it. AED is $350, Lund is $300. You will get a tune for 91/93, a fuel pump tune that will allow you to run the fuel pump without the engine on to manually drain the tank, and the E85 tune.
Be prepared for an awesome smell and horrible gas mileage. I average about 17mpg on the highway at 70-75mph and about 14mpg city, if that.