You can get quite reasonable results using a brush - particularly on the smaller models.
Here's a brush painted 1:72 Airfix Bulldog.
It is the larger models - where you have large surfaces to cover that an airbrush really comes into its own. However, you would do well to gain a bit of experience using brushes before switching to airbrushing.
Ships are really my thing and there I tend to use airbrushing for the large surfaces (hull / superstructure), and brush for everything else.
As regards Airfix kits ...... the more modern ones I find are a delight to build. Some of the very old ones are a bit of a challenge and need a fair bit of work...... but I enjoy working on them. At the end of the day I feel I've actually built something rather than simply knocked something together.
I suggest you discuss what you are after and what you are planning to buy or building here on this site and I'm sure you'll get all sorts of help an advice.