Firstly, Congratulations on your pregnancy!
With bras, I am small chested, so I didn't need a maternity one for quite a long way along, however, one good piece of advice (I got) was to ditch wearing any bras with an underwire, especially once breastfeeding.
This will sound weird and embarrassing for me to say, but I had no idea that all the extra blood pumping around your body may cause you to be extra, how shall I say this....amorous! Obviously not everybody will be h...y as hell pregnant and I am definitely speaking from second trimester onwards, but I know I was *blush* and it came as quite a shock to be honest.
Maternity clothes, I mainly just bought normal clothes and depending on the style would buy a size up and odd maternity outfits here and there, but I did splurge a bit on some nice maternity jeans like Seraphine and 7 for all mankind to name a few, as they don't look 'maternity' perse and I would wear them post birth till I felt comfortable in my normal jeans etc.
Other random things that come to mind are the relaxin helps your teeth move, so if you are wanting braces, pregnancy is a great time to get them and lessens the time you may need them on.