Advice: Converting 7-speed freewheel to 8-speed cassette

Hello everyone. Currently I don't own a bike but I want to buy one for commuting, and I have some basic knowledge of bikes and their components. The commute is around 7 km (4.5 miles) each way, but in hilly terrain. My local bike shop has the Giant Escape 3 model 2016, which I really like, however, this bike comes with a 7-speed freewheel which is really 6-speed plus a larger sprocket (sprockets 14-16-18-20-22-24-34). I don't like that gap between the two easiest gears, considering the hills I would tackle. The seller mentioned that they can swap the wheel hub for one that would accomodate an 8-speed cassette with 11-32 sprockets, and changing the shifters, but keeping everything else as it comes, including derailleurs.

In your opinion, would this work? I like the idea of the 8-speed cassette with more favorable gear ratios. What should I be aware of?