Welcome to IIS Boxy.
A few thoughts on your questions:
- The barlow is not something to take lightly. Save a bit longer and get a good one and it will serve you for many years to come with any scope you happen to have at the time. In the 1.25" range the Orion Shorty Plus is a beauty but it is about $140 from Bintel so more saving is needed. Remember, a bad barlow is an expensive paper weight.
- Deep sky filters chew up light as they only pass a small fraction fo the light gathered through to your eye. They work well on scopes of 8" and above with the emphasis on the "above". I use them on my 8" for some objects but I have to be a bit picky. I would suggest you save your money for the barlow.
- Bintel are great, I have bought lots off them but they are not the only good supplier in Sydney and its worth checking around.
Keep looking up