Thank you all of your comments, both positive and negative.
One thing I neglected to mention but should have included in my initial post is that I created a Commsec account in December - this gave me $600-worth of free trades so my four purchases haven't cost me a penny in terms of brokerage. Of course, they might cost substantially more if they all go south!
I went with Commsec because a friend who invests (he's the one who sparked my interest) uses it. I checked out the website, which seemed straightforward, so joined up. I did consider other online brokerage site, so I am prepared to move around to take advantage of various offers and better service. I should mention, though, that I have been very impressed by Commsec's customer service to date - my $600 of free brokerage was not applied, but a quick phone call addressed the problem. The staff also followed up an email inquiry very promptly so I have no complaints.
As for what kind of approach suits me, it's definitely long-term investing as I have neither the time nor the nerve for day-trading. At the moment, I plan to limit myself to a small number of companies - four, perhaps five - and invest for the long-term, take the dividends, small though they are, and hope for capital gains.
I do have more to invest (around another $30k potentially), but as I still have a great deal to learn, I am definitely keeping that in reserve for the moment. I will, of course, add to this sum as I continue to save, but I feel that $4k is enough to spend as a way to familiarise myself with the markets. All going well, however, I do intend to invest more in the future through private investments, funds, and government bonds.
Hopefully my timing won't prove to be terrible! I am prepared to hold on to these stocks for the long term, so hopefully that will help me ride out any fluctuations. Regarding MFG and TOL, I know both are a bit of a risk, but I'd counter that by arguing that all investing is, and that I am reasonably confident in their long-term trajectories for the reasons I outlined in my opening post. That said, I would be lying if I said that it hasn't crossed my mind that both may have peaked. In the defence of TOL, at least, I'm comforted by the fact that it has historically been higher (around the $10 mark). I do intend to watch my stocks closely and my 'getting out at -20%' rule should insulate me from massive losses, unless the stocks collapse within a day.
As for the numbers, I ended the week up by a little over $10. A paltry sum, no doubt, but a profit is a profit! Long may it continue.
Anyway, I hope I've answered your questions, Thraxier, and thanks to everyone else for their comments. It's great to get a broad range of comments; it certainly gives me something to think about.
Good luck for the coming week everyone. I assume that the U.S. sequester will have a negative impact when the markets open on Monday, but hopefully it won't be too drastic and the recovery will continue.