"Total Used Margin" does not represent risk.
For each trade, risk is determined by the size of your position, the pip-value of the pair you are trading, and the depth of your stop-loss.
To see why this is so, consider three identical trades in three different accounts.
Let's say the trade in this example is:
Long 1 standard lot (100,000 units) of EUR/USD, entered at 1.0600, with a 50-pip stop-loss.
(1) in an account requiring 2% margin (corresponding to 50:1 allowable leverage)
(2) in an account requiring 0.5% margin (corresponding to 200:1 allowable leverage)
(3) in an account requiring 0.1% margin (corresponding to 1000:1 allowable leverage)
In account (1), used margin is $2,120 (that is, 2% of 100,000 units x 1.0600). In account (2), used margin is $530 (that is, 0.5% of 100,000 units x 1.0600). And in account (3), used margin is $106 (that is, 0.1% of 100,000 units x 1.0600).
But, in each case, risk is $500 (that is, 50 pips x $10 per pip per standard lot x 1 standard lot).
True risk, in that case, would be limited by the point at which your account suffers a Margin Call. That's the point at which your broker automatically closes your position to save you from a total wipe-out of your balance (or, worse, a negative balance), and to save himself from having to chase you to collect a negative balance from you.
You should avoid margin calls (by limiting the total risk in all your open positions). And, in order to do that, you need to know exactly how your broker imposes margin calls. Not all brokers are the same in this regard (or in any regard). Read the Terms and Conditions of your account, or ask your broker directly.
MG99 doesn't use stop-losses in his Portfolio Methodology, but many of the other traders commenting on his thread do use stops. The stop-loss tactics you have described above are reasonable. BUT, if you are a brand-new swing trader, trying to use the MG99 Methodology may be a bad idea. Here is something I wrote on that subject ---