re: What are your trading strategies?

What vehicle are folks trading in?

The reason I'm asking is - My sense is that it's smart to limit the number of positions in a Roth due to the contribution limit. Ie. If you have 10 holdings in your Roth, and want to increase your holdings in any real way annually, $5,500 per year won't really allow you to do so. Up to this point, my only investment vehicle is my Roth. (26 years, only been investing for 3 years)

I'm self employed and am considering opening a SEP or simply a cash account in order to start doing some real damage in terms of accumulating significant positions. Leaning towards a SEP because of the tax advantage and I don't already have a 401k through work.

Any reason a cash account would be more advantageous than a SEP? Feel free to shoot down anything I said above.