Well, I do not know how other people here play venom mages but my first priority is not getting Venom Bolt doable. With a mummy this is true even more so because of it's crappy aptitudes. It would mean you would rely on Sting longer than it is healthy to do so.
And this especially if I do find a good weapon early. ANY branded weapon is good for MuVM and worth considering starting training. Even protection branded weapons.
The thing is that if you start mummy venom mage, you are not necessarily relying on poison damage for very long if you do find a good weapon. Or a better conjurer spellbook than the one you're starting with. Getting Meph castable is a good goal but while knowing it is very loud and doing minimal damage, you do need melee or other spells to hurt monsters more. So if you find that elec dagger, pick it up and start swinging it, and demote sting as a softening attack.
Again, this is a very hard combo to give advice on just from a get-go.
EDIT: and oh yes, cast mephitic cloud even with high spell failure, if needed. I do use it regularly by the time it is about 20% fail rate. If you don't mind the noise: killer bees, orc wizards and priest are excellent targets even with 20% fail rare. 30% if you really wanna put your mana/luck at the test