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Improved familiar is fun, but unless you're going to utilize UMD on some wands to try to get more action economy, or you have one of the archetypes out of the familiar folio (eldritch guardian fighter and chosen one paladin especially) they aren't "optimized"
How much this matters depends on the game
I like improved familiar
On my casters I treat it like how I treat weapon focus for my materials (also like I treat spell focus)
It's a good filler feat if you can't think of anything better
You don't have to have a familiar at all, and if you're not sure what you want it for then spending 3 feats is way over the top. If you want a scout or messenger then a figurine of wondrous power, periapt of temporary familiar or a migrus locker, or a spell like draconic ally may be better. If you want to deliver touch spells at range look at the spectral hand spell.
I concur with AVR; figure out what you'd use a familiar for first before you decide to take a bunch of feats for it. If you're looking to exemplify using scrolls, maybe take a look at Cypher Magic which gives you a +1CL bonus and +2 on checks to activate higher level scrolls.
If you eventually want the familiar reading your scrolls, consider the following winding road to success:
1. Take a familiar that can speak; give it the Valet archetype so it can Prestidigitate (slowly manipulate 1 lb of material) a scroll
2. Take the feat Evolved Familiar - Skilled to give the familiar +8 Use Magic Device
3. Swap the familiar's starting feat with Extra Traits; take Dangerously Curious as one of your familiar's new traits
4. Take the 2nd level spells Eagle's Splendor and Visualization of the Mind
5. Take 4 ranks in Use Magic Device
Follow this program every day:
1. at daybreak take 1 hour to cast Visualization of the Mind (Charisma) on your familiar; the familiar now gains +5 on all Charisma-based checks
2. Before combat if you think you're going to utilize your familiar's scroll-casting abilities, cast Eagle's Splendor for a +4 Enhancement bonus on your familiar's Cha
At this point your familiar should be at +21 Use Magic Device: +3 Class Skill, +4 Ranks, +8 Evolved Familiar, +5 Visualization of the Mind, +1 Trait. The familiar likely starts with a Cha 7 (-2 penalty) so casting Eagle's Splendor simply removes that.
So with UMD +21, Speech, the ability to hold/manipulate the scroll and no auto-fail on using skills for rolling a 1, this means that your simple animal familiar is guaranteed at successfully casting spells from a level 2 scroll or less. Since all you can write is a level 2 scroll spell, you should be just fine.
Remember to think about the story and flavour, not just optimising your build mechanically; this is particularly important with something that has as big an effect on the game as introducing a new familiar should. In universe, they don't just pop into existence because your character took a feat, you know!
What part has* the original familiar played up to this point? Why is your sorcerer willing to destroy that bond and form a connection to some new being? Did the previous familiar get killed, perhaps? Or fail your sorcerer one too many times? Or is it still the same familiar, only now with its true form revealed (as in the Chosen One paladin archetype)? There are lots of interesting ways you can take the concept of a familiar, either improved or not, but if you're just looking for some extra mechanical power I'd advise you to skip the familiar and spend your feats on something which doesn't come bundled with a bunch of extra rp flavour. On the other hand, if you can see a way to make your character more interesting or fun to roleplay as by using a familiar, do so! And you'll probably find that exactly what your idea is will help you decide whether Improved Familiar is suitable for you or not.
*or will, if you're planning ahead in your build; I'm not entirely sure from your post.