EL really isn't that great. It's not very bright, it's not exactly cutting edge technology.
Blue EL sheet... easy to source. Cutting into individual letter shapes... can be done with a stanley knife.
That's the end of easy....
EL sheeting is a layered product. The centre core is the illuminated membrane; either side of this is a layer of clear protective film which waterproofs the sheet. You'll also see a couple of thin copper tracks which carry in the electrical juice.
When you've cut up a stock sheet of EL into a numeral shape you've destroyed the integrity of the water proofing and you've also cut off the power terminals. Re sealing the EL is a pain, trying to dig out the terminals which have been laminated into place is almost impossible. To do what you want you would ideally need a raw piece of EL membrane which has not been laminated with the copper terminals supplied loose... something I doubt you'll be able to get your hands on.
The power characteristics of EL aren't as simple as they sound; yes you can use a low voltage DC battery but the EL sheet works at much higher voltages than 9vDC. When you switch on an EL display of any size you hear an annoying high pitched whine which is the power convertor jumping the voltage up to a high enough level to get illumination. I also dimly recall some issue with DC to AC conversion, (it's been so long since we evaluated and rejected EL that I can't remember the exact details).
The biggest issue is light... or lack thereof. If you want to take all your product pictures in pitch darkness it's not hard to make EL look like the cats pijamas; introduce even a moderate amount of ambient light and your illuminated EL vanishes under the weight of lumens being dumped by the lighting all around it. In a busy, floodlit sports stadium I doubt you'd notice a fully illuminated EL number unless you were 3" in front of it.
If you still want to go with EL I would clarify the electrical consumption, voltage and amperage. I'd also ask for the ambient lumen value at which the EL becomes swamped.