For Paragon Paths, consider:
Lyrandar Wind-Rider and Arcane Admixture on your Elemental bolt. 2 feats and your PP for a +1 to hit, and applying your secondary to damage.
Crimson Hunter. 1 feat (your MC slot, though) for a +1 to hit, and an expanded critical range at 16.
If your DM houserules/handwaves Academy Master into a functional state, then it is also a pretty good choice for an Elementalist.
The other issue with Crimson Hunter is that it requires multiclassing Seeker, when Wisdom is the best ability to tank- it stacks on defense with Charisma. You'd have to start with a 12 in WIS to take it as a PP, when you can just as well start with an 8 otherwise.
Depending on how you do the build, Essence Mage comes into play- Arcane Admixture on the Elemental Bolt is already a nice way to bypass resistances, so you'll get the extra 1d6 on it, and the Action Point feature means that you're pretty unlikely to miss during that round. Make sure to take the AP before doing anything else, though. You can take cold damage and build in permafrost, either with Lasting Frost or with Arcane Fire.
As for Weapon of Speed- you should keep it up to date, but you're likely to take Dual Implement Spellcaster anyways, so you might want to keep it in the off-hand. You might want to consider something low in each tier (like Wyrmtooth, 2+) rather than something high (like Elemental Twist, 5+), so you can potentially get the upgrade earlier. Once you hit Paragon, Melegaunt's Dark Blade and Jagged Weapon are both worthwhile looking at, especially if you have AA or something else to help ignore resistances/immunities.
One other trick- keep in mind that Ignition, while an Arcane fire attack, doesn't actually do fire damage. The same is true of Blazing Starfall, which you can take at 9 (radiant damage). That's potentially useful when dealing with fire resistant/immune enemies.
