Learn English – Expressing mixed feeling of both scared and sad

This is really a question about style rather than grammar or usage or even word choice.

A better sentence is:

They are all similarly dressed up for the party.

or

They're all similarly dressed up for the party.

A different word order changes the sound and rhythm of the sentence. The version with the contraction is more natural and idiomatic than the one without it.

I agree with WendiKidd that "similarly" and "alike" are not equivalent, so "dressed up alike" neither says what you mean nor means what you want to say.

If by early, you mean that you want more time from him to make a decision, (that's what the situation tells me), I'd recommend a legitimate use of

Sorry, but as you see choosing the [an adj that describes the quality of the way you choose the best; e.g.: optimum, most productive etc.] way is hard to do instantly/at the moment. I'll need more time to put my thoughts together and will be able to respond in ...