It's listed as a male half-orc name in 5e PHB.
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[RPG] How to pronounce “Mhurren”
dnd-5ehalf-orclanguagespronunciation
Related Solutions
There's a pronunciation guide on the Wikipedia Page, which references an old FAQ, for whatever that's worth. Essentially it's pronounced how its spelled, no real trick to it.
Might help to think of it as "Smurf-Neblin", only with a V instead of the M in smurf. Doesn't really roll off the tongue no matter how you pronounce it, but I'd guess that's half the point.
It should also be pointed out that this is the name that the Deep Gnomes have for themselves in their own language, not necessarily what anyone else calls them, so you shouldn't feel obligated to use it all the time. More likely it'd be used among themselves, or by people that are trying to make nice with them, such as merchants or diplomats.
This is a DM call.
As observed in another answer from Thomas Markov, there are two ways of reading this.
The first reading is literal: the Fireball is centered on yourself, hence the point of origin is the center of the square in which the characters is. The situation is depicted in the below figure, where the green circle is the Sorcerer, the red circles represent other creatures and the small circle the point of origin of Fireball.
The second reading applies the rules for using a tactical map from the DMG and the rules from XGTE:
Choose an intersection of squares as the point of origin of an area of effect, then follow the rules for that kind of area as normal (see the “Areas of Effect” section in chapter 10 of the Player’s Handbook). If an area of effect is circular and covers at least half a square, it affects that square.
In this case, there are 4 intersections around the square in which the Sorcerer is: then it has to be decided from which intersection the Fireball originates. The 4 situation are depicted in the figures below: pay attention that this choice affects in different ways the creatures around the Sorcerer.
North - east corner
South - east corner
South - west corner
North - west corner
It is up to the DM deciding who picks the point of origin: the player or themselves.
Best Answer
If it is assumed to have a Celtic/Gaelic origin, then it is pronounced "vurren" or "wurren".
Most of my examples would come from the names of Scottish mountains - e.g. Sgurr a' Mhaim, Sgurr Mhurlagain, Sgurr Mhic Coinnich, where the Mh is pronounced "v". (See here for spoken examples.)
In Irish gaelic is would be more of a "w" sound when occurring at the start of a word: "wurren" (e.g. see here.)