Need electrical help on building a 5 liter-capable sitr plate

A little background on me - I'm a pretty decent DIY guy, but electrical theory (resistance? ohms? watts?) is an area I know jack and squat about.

I wired a large portion of my house, including a couple of three way light circuits (though I will confess to cursing them more than once). I'm building an STC-1000 temperature controller box; piece of cake. I'm pretty confident that I can build a stir plate.

The thing is, most of the builds I see are for 1-2 liter plans. That's fine, but I plan to start getting into lagers, so I'd like to be able to do monster starters.

As I understand it, I'll need to purchase a stir bar. Any recommendations on size?

I have plenty of rare earth magnets (I'm an IT guy by profession, so I have all the dead hard drives you can shake a stick at).

I've picked a large, sturdy project box.

Here is the fan I'm planning to use.

Where I start to get confused is when we look at power supplies and rheostats. Do I need a 9v power supply? Something else? I figure that I can probably scavenge a power supply, but I'll buy one if need be.

What about a rheostat/pentiometer?

I see 3 watt, 25 ohm rheostat mentioned on a lot of builds, but these are typically for smaller stir plates. Will that still be fine for a bigger one?

Also, I can't seem to find one of that size at amazon. I'd really prefer to just order it all from them. Explain like I'm five - what difference do the watt/ohm ratings make?

Thanks for your help.

The 120mm fan that you are thinking of buying, doesn't spin nearly as fast as the smaller 80mm version. I found that out, searching through diy stirplate threads on here, but I can't think of the thread name at the moment. Something to do with the RPM's.

I use the 80mm thermal take fan for my stir plate, and will tell you its very powerful. I just did a 3L starter in a gallon growler, which has an uneven bottom, at the lowest speed, with highly flocculant yeast. Since that worked, I have no doubt a 5L E. flask will work. You may benefit from a 1" stir bar, or larger. I have a small one stirbar and it works great. From my understanding, the starter just needs to be moving the yeast/krausen around, it doesn't benefit from a huge vortex in the middle.

You don't need any of the other components, that you mentioned, only a spare cell phone charge adapter, for a usb. The fan comes with everything all wired up, including a speed dial. That's why I bought the thermal take fan.

The main thing about the stir plate, is that your magnets are as close to centered as possible. It was hard for me because everything was so small, and I was using super glue, that dried instantly. I couldn't adjust anything, after it was set down. I said many curse words during the making. Here's some pics...

I appreciate the input, thanks!