I'm a writer and a graphic artist. I've just started to create my comic novel, but I believe it's feasible to do all the work by myself (With the exception of the editing of the script as my co-writer did that.). I'm aiming for app. 100 pages in the first round.
Based on my present experiences as I already have most of the designs for the world, I would say 1-3 panels per day. Maybe 4 (Black and White. Coloring them takes a bit more. Hmmmm. Let's say 1-2 panels per day if you're coloring them and 2-3, max 4 if you're making B&W draws as I do them now (Less if I want to do the panels to extremely detailed.). Well, as an artist I can work relatively fast, while I can keep the quality. But maybe someone can do the arts faster, someone can do them slower as I do. So, it's depending from the artist (By the way, your arts on your homepage are pretty nice.). As for the scripts... the time of writing is depending from your skills or the usual "Do you have an idea or not" phase. Actually this one is depending from various circumstances.
Is it worth it? Maybe. Maybe not. No one knows that for sure. It's depending from the genre, from the quality, from the execution... so from many details. And even if it's flawless, there is still a chance the project may fail by various other circumstances. It's worth to do this for one thing which is sure... experience.
I believe it's not impossible to be the writer and the artist in one at all. But what I write is just based on my personal experience. Maybe someone else, who actually finished a comic novel already, can tell better estimations and may see things different.