The thing you need to look out for in Illusion is that it requires tons of GM buy in. You will need to find out how he rules the different types of Illusions.
The issue with trying to be good at two things is that when you're faced with an enemy that has 100% invested in one thing, you won't match up to it.
On top of that, trying to fill multiple roles, even as a Spellcaster (who is the easiest to do this with), essentially makes the group turn to you, and it becomes problematic because when both roles come into play, the action economy works against you. For example, if you're faced with two options, of only which one you can take, something bad will happen throughout the round that you couldn't prevent, primarily because the group is throwing too much expectation into one party member. This is the same flaw as to why single-creature boss fights are flawed.
That being said, if you aren't opposed to a "Jack of All Trades" playstyle, take a look at the classic Bard as an example of playstyle to follow: He provides buffs, excels at practically every skill in the game, and can throw some damage out if needed, but outside of those 3 things that he can do, he can only do one of those better than any other class, and that's Skills. (Bardic Performances count too, but that encompasses other things beside skills.)
A spellcaster is a lot more of a blank slate, the Sorcerer even moreso, because the features don't define the class, or the player in this case; the player defines the features (and therefore, the class and niche they want to fill).
With that being said, you declared what you wanted to be able to do, which is Illusions + Fire Blast spells. Depending on what you want to specialize will determine what choices I can present.
For example, the Orc bloodline, at its base, will provide a better benefit for blasting, as it deals increased damage based upon the number of dice you roll for your blast spells, something which outweighs the minor utility and defensive components that the Elemental Bloodline grants.
For Illusions, the Undead bloodline is one of the better choices, as its base benefit allows you to affect Undead (if they were once humanoids, which as far as the all-powerful Liches are concerned, they meet this qualification) as Humanoids for your illusion spells, an effect that not many things can accomplish. Additionally, the later levels provide forms of CC that aren't pure illusions, and this is important to consider as an Illusionist when you're faced with the biggest counter to your school, the True Seeing spell.
As for feats, Point Blank Shot is really only important if you plan on specializing in close-range combat with spells that rely on attack rolls to work, which is a single target Blaster-type feat. Unfortunately, if you really want to make this work with your half-level BAB, you're going to need Precise Shot as well, otherwise you're going to end up missing a lot more, as well as accidentally hitting your friends with your damage spells.
The elemental focus also only matters for spells that have the listed feat in their descriptors (in other words, unless a spell is a [Fire] spell, the feat won't apply). I would actually suggest Spell Focus (Illusion), as several of your Illusion spells that are extremely powerful, such as your Color Spray (and later on, the Prismatic spells), are usually going to be Save or Suck/Die. Making those work more often will be more important as far as consecutively doing something worthwhile each round is concerned.
But again, this all boils down to if you want to specialize in one thing, or be a Jack of All Trades.