Dumbell's are a good start off, thats how I started doing weights. They really tone your fore-arms and biceps, I have trouble with them now though as I broke my left wrist a few years back.
The amount of weight is entirely up to you. I use 16kg Dumbells, anymore my wrist will literally snap. But you may be able to up, or need it lighter if you are starting out.
As for the barbells. Start at like 10kg on a standard press and raise it by 5 if needed, you'll generally get stronger with time. But technique is the key, always. Reps of 10 will tone you 12 will work your fitness and 15 will make you stronger. You can also use the barbells for Biceps, I find that I can do half of what I can do on my chest on my Biceps.
I'd recommend machine weights as you can work on all your body, legs, abs, arms, shoulders, chest and on...
You could also look into drinking protien? Not everyone's cup of tea but something you should consider. I'll not go into creatine as I disagree with it.
Just be sure to work on your knees as more weight top half will need plenty of support underneath and thats were knees come into play
As for brands, I recommend
York Fitness and
Marcy Fitness. JJB or Argos, or anywhere really!
Edit: Also, punchbags are an unbelievably beneficial workout for balance and strength and calorie burning. Everlast is the best make for that stuff.
Coming from a Rugby lad, James.