Hi Tyler - My fiancee and I just returned from a trip that included 4 days in the CT and I can definitely confirm the Corniglia-Manarola section of the coastal trail is closed (we didn't know and hiked to the gate).
On our first full day we did trail 7a that goes from Corniglia to Manarola via Volastra. I thought that trail was great, and it offered nice views along the way. It takes a lot longer to hike that segment than any of the segments on trail #2, though, and is more crowded than usual b/c of the #2 closure. The alternate route from Manarola to Riamaggiore is VERY steep up and down, but doesn't take a ton of time if you can keep putting one foot in front of the other. It's a little tough to recommend hiking from Monterosso to Riomaggiore in a day if these two trails are still the only real options when you get there. We hike pretty often and are in good shape, but I'm happy that we split it up into two days.
Other hikes: 8a is closed, and has been for a while, but if you want some moderate route-finding challenges (there are faded or overgrown blazes) and an empty hike it's the way to go. There are three or four parts that are washed out and make for tough going, but overall it's still in great shape. It's a great loop that starts and ends in Vernazza and goes through the great little town of San Bernadino (which offers a steep descent to Vernazza). You'll cross streams, see some small waterfalls, walk through terraced olive orchards and vineyards, and get great views of the hills above Vernazza. Also, a short detour takes you to the Sanctuary above Vernazza, which is very nice to visit.
The hike from Riomaggiore to Portovenere sounds great, but we didn't have enough time to try it. You might consider reading up on that one. If you do it early in the day it should be easy to hitch a ferry back.
Edit: Re: the 9am open time poses no problem for hiking. We hiked every day before 9am and it was no issue. When we got up early to go from Monterosso to Vernazza we just bought our hiking passes at the kiosk in Vernazza, which was just opening when we got there. It is not like you will contend with closed gates or anything. You can also buy the train + hiking passes at the train station the day before and validate them in the morning I guess, but it really is tough to get your money's worth out of those combo tickets.