I haven't done the race but I've cycled a fair bit in this area of Switzerland. From the start of the bike until the foot of the first real climb in Airolo (Gotthard) you're climbing 1000m over 80k. The first 40k you're maybe climbing 150m, that's basically flat. The second part you're climbing the other 850m so that's a bit more but still around 2-3% average. You can probably make very good use the aerobars here. Likewise, the last 20k from Innertkirchen to Brienz are flat in the valley save for that little 1k climb over the Aareschlucht. So all in all that's almost 100k of possible aero time ;)

As far as the descents: Gotthard northside is not very techinical at all, only a couple of turns. Expect headwinds. Furka descent is amazing, you see the Grimsel in the distance, it's a sublime panorama. There are some hairpins but again no tunnels and not very technical, mostly fast and straight, and of course great road surface. The long descent after Grimsel is also fairly straight (also some flat sections along the lakes, again some aero time), some hairpins on the higher sections right after the top. Here there are some tunnels, but they are mostly straight. When you're climbing the long side of Grimsel you can take a detour around some of the longer tunnels, they are great little roads literally hacked out of the side of the mountain in certain places, but for descending, not advised. The road surface is not as great and oncoming ascending cyclists are likely not expecting fast moving bikes coming toward them. Just bring some lights and you will be fine in the tunnels. Traffic in general is not as heavy as it is in other countries I've found.