30 watts isnt that much, but its enough to get you going, and more than enough for practicing by yourself.
I had a marshall 25 watt amp in the past that was almost inaudible, but i think it was dodgy to be honest.
One wee practice amp i like is the Peavey Max110 and the Ashdown AfterEight (the larger models are also quite nice), got my better half one for her birthday. If you look used you can get a practice amp for sub-£50.
Ive never owned one, but i know alot of people who have, and yamaha makes really good basses right across the spectrum!
You'll need an instrument cable to connect the bass to the amp, you'll only really need a bag if you are taking the bass places, but it is useful to have, a strap would also be very useful.
For tuners, i like the korg GA-30, costs about £10.
using picks is a personal preference, alot of people will play bass just with thier fingers

As you are just starting out, it might be useful to buy a few different type and sized picks, to find which you feel most comfortable with.