I don't have much to say about the online personas part, but I feel you on the difficulty of branding! My boyfriend's dad helped me come up with an excellent name for my business - short, catchy, allows me to expand - but the other aspects are still such a pain.
As for pony personas without symbols, I'm another vote of go for it! My ponysona is a pegasus with speckles on her rump and wings (plus a few other small wing markings). She used to have a symbol but I kind of got bored of it. Real people are very hard to sum up in a small, simple symbol that's easy for artists to draw. If I ever get a custom of her I might get a TAF style symbol on the NDS that incorporates all the stuff I love, but when it comes to drawn sort of art I prefer her to be simple.