I can only say is to educate yourself on the plenty of info online....I bought my 1st bike as an adult at a LBS in '83 and can now say that bike was too big...but I still enjoyed it for 7 yrs.(then none for 20) And about no hills in FL...nothing but hills in Talllahassee!
If you like to work on stuff yourself a bike is no problem! I've just installed a 11spd IGH on my Trek Sawyer and didn't even know what IGH was 14mths ago and disc brakes too! I've ordered 4 of my bikes without test rides. I have to admit I was lucky with the Kona and almost went a size too small. I've order from Bikes Direct ...no tax and free shipping and check out there Scratch & Dent site Bikes Island...I got a Motobecane Jubilee 8spd nexus IGH for $299 (just as fun as my other bikes)

The main thing is to google any bike for reviews and parts for that matter. Plenty of instructions on youtubeI...I have nothing against LBS...but live too far away and the ones that are 30 + miles (can blame big University too)