I like the comic so much! And I would like my character to be in "The Feast of Nero". Is it possible?

No. Strictly no.
But, soon I will create bunch of YCHs with the characters from "The Feast of Nero", so it will be nice opportunity if you want to get your character painted with the characters from "The Feast of Nero". As soon as new characters will appear in the comic, I will create more YCHs featuring them!

In which historical period the events of "The Feast of Nero" take place?

"The Feast of Nero" takes place between 51 and 63 A.D.

Is Servius a wolf?

No! My beloved Servius is not a wolf. He is a coyote. (Yes, I am aware that coyotes do not live in the area of The Roman Empire :) )

Is it possible for a canine like Servius to impregnate a feline like Julia? Seeing how they are smitten with each other.

Yes, it is possible. This is why Julia mentioned Silphium – a plant used like a contraceptive potion. Silphium is not as effective as modern contraceptives (if effective at all), but still.

The breeding logic of  Furry Rome World has the conventionality: different species can have babies together, but with a strict rule – the offspring can never be mixed between different species, so children will strictly take the form one of two parents. Like, there will be no hybrids between cheetah and coyote, but their babies will be cheetah and/or coyote.
There is still a natural, physical limitation for breeding between different species, like elephant male cannot get babies with lynx female, because penis of elephant is too big for lynx. And so on.
So please, keep in mind the conventionality above. In addition, all my stories are focused on Roman customs and life, but not on subtleties of reproduction.

How many pages in total "The Feast of Nero" will contain?

I think not less than hundreds.

What do the carnivore citizens of Furry Rome World feed on? Their herbivorous fellow citizens?

Of course no :) Furry Rome World has cattle, wild game, and everything tasty that a real ancient Rome had.