Since you're already commuting with your current bike, it has probably given you some clues about it that you like and don't like. Your next bike should address the things you don't like about your current one. But you may not need another bike. Sounds like your going to give LCF a go and from you're stated daily range of no more than 25 miles (accumulated throughout the day and not all at once, correct?), then the bike you have should be sufficient- as long it is a good fit. Wouldn't hurt to have a back-up bike, though .

As far as what to wear- what ever you're comfortable in, whether full kit or gym shorts or sweats.

Consider investing in some Ortlieb panniers if you ride in the rain a lot or Arkel if you don't mind messing with the rain cover.

If you want more input on the bike selection, you need to provide more data- like hills, rain/snow, storage inside or outside, ride on asphalt, dirt/grass, or a mix?