As above - check out The Bass Player along Parramatta Rd at Annandale. They're on the left side, 50 mtrs past the Johnston St-Parra Rd intersection, as you head for the City.
Yeah, I also gotta agree about 5 stringed Bass. You're a bassist and therefore only capable of handling 4 strings max! Even then, we usually play only 1 string at a time. Hehehe j/k 'cos I play bass also.
Unless you need masses of power, a good single 12-15inch speaker with built-in amp of 80-200W would be more than enough to practise and have some small gigs. Something like a Crate or similar brand will get you a reasonable amp/spkr. When you start to become fabously famous and rich (from your music) you can then go and buy the big expensive stuff.
Valves or trannies? It's sorta like the EFI or carbs argument - both work and do the job and everyone has their own preference.