That calculator on Mr. Malty (see link in previous comment) will tell you what volume of starter you need based on the parameters of your wort. I put in an OG of 1.082, batch size of 5 gallons, yeast mfg date in mid-May (Wyeast has it printed on the package, White Labs uses a "best by" date instead that you have to work back from to get the rough mfg date). If you use a single pack of yeast, it says you will need a 5+ quart starter. You could do that, or do a multi-step starter (very easy, just takes longer), or use a smaller starter with multiple packs of yeast. Your choice. But I'd definitely put the info for your batch into the calculator yourself to double check me.
As for the container, an Erlenmeyer flask is not mandatory. I use a 1 gallon glass fermenting jug. As long as you use a sanitized, food-safe container, you will be fine. Also, stir plates are useful, but don't worry if you don't have one, you can still do a simple starter and be just fine.