It sounds like you're eventually going to end up with a rig similar to my own, so I will chime in here with some basics about my equipment and process.
Equipment
Mash/Lauter Tun I took a keg like yours and added a Zymico weldless conversion kit to it. This gives a ball valve and barb on the outside of the keg as well as a threaded fitting on the inside. Connected to that fitting, I have a stainless dip tube and false bottom.
Some people have issues with grain sneaking under the false bottom, but I don't. I think two things contrinute to this. First, the false bottom I use is not simply a flat piece of steel. In my experience, these are never quite flat, and they don't form a good seal to the bottom of the keg. Instead, mine is somewhat domed at the center, then has a turned-up lip which fits quite nicely into the bottom of the keg. Second, I added a stainless hose clamp around the dip tube to keep the false bottom from rising more than about 1/32".
Hot Liquor Tank This is another keg with a weldless conversion, but the inside just has a simple dip tube that goes down to the pickup well at the center of the bottom. It never has anything except water in it, so there's no need for any kind of filter or screen.
Boiler In contrast, there's all kinds of crap to filter out of the boil. I was concerned about trapping wort under a false bottom, so I opted to used a Zymico Bazooka tube as the screen in this one. I did make a custom dip tube arrangement for it to get it as close to the bottom as I could, as I was leaving too much wort behind. This filters out hops and break material with no problems.
Burners I have three of these, on stands I welded up out of angle iron. You can get by with only one, but you will be lifting hot, heavy things up and down if you choose to do that. If you have burnrs but no stands, you can use tables, bricks, terrain, etc. to form your tiers. I use a two-and-a-half tier system with one pump to reduce overall height of the rig, but three-tier systems don't need any pumps at all. Arrange the boiler at the bottom at such a height that your outflow can be easily directed into your fermenter. Your mashtun goes in teh middles so it can flow to the boiler, and your HLT goes on top so that it can flow to your mashtun.
Sparge Device I use a fixed sprinklerhead in a wooden frame which sits on top of my mashtun. I tried the Phil's Sparge Arm and had issues with it. I've also done the aluminum-foil-with-holes-in-it thing. So far, the current setup works best. Your milage will, of course, vary.
Chiller I use an immersion chiller I made from 50 feet of 3/8" soft copper tubing.
Mill You don't have to have a mill, but it's a nice touch. Really, all you need is access to a mill. Your FLHBS probably has one you can use.
Process
Calculate I have a spreadsheet I use to calculate my mash volumes and temperatures based on my grist weight and water:grain ratio. The calculations are not terribly complex, but do require some work with a pencil. My spreadheet is based on calculations in The New Complete Joy of Home Brewing. There are also online calculators you can use.
Mill Grain Again, this may be done for you at the shop.
Measure and Heat Strike Water I fill my mashtun with water using my graduated mash paddle to measure, then fire up the burner. In general, I dough in with 1.25 quarts of water per pound of grain, and heat it to about 163 degrees F. I pour in my crushed grain and stir well, breaking up all the doughballs I can find, then leave it alone for 60 to 90 minutes.
Measure and Heat Mashout Water As the mash winds down, I heat water for mashout. The idea is to raise the temperature of the grain to 168 degrees to stop enzymatic activity. For a 25-pound mash, I heat about three and a quarter gallons of water to a boil, then add this to the mashtun and give it a quick stir.
Measure and Heat Sparge Water For the same 25-pound mash, I'll need about four and three-quarter gallons of sparge water. This get heated to 175 degrees or so, and the sparge device gets set up.
Vorlauf I recirculate a few quarts from the bottom of the mash to the top. This removes any particles that snuck past the false bottom and sets up the filter bed. Then I set up the tube from the mashtun to the boiler.
Runoff I crack the valve on the mashtun to allow a nice slow runoff, and allow a balanced amount of sparge water to flow in from the HLT. It should take about an hour to run off enough wort to fill your boiler.
Heat Toward Boil Fire up the burner under the boiler and get cooking. I skim the dull-colored protien foam that rises - it helps to prevent boilovers and seems to result in clearer beer in the glass. As you get close to a boil, you'll want to be ready to kill the heat at a moment's notice - boilovers happen FAST in homebrewing.
Boil Follow the recipe's schedule here. I typically boil 60 to 90 minutes, making several hop additions along the way. You'll still need to keep any eye out for boilovers. Use just enough heat to get a nice rolling boil so that everything swirls around in the pot. It's worth noting that my rig doesn't like pellet hops - the sludge gums up the Bazooka tube - so I use only whole and plug hops (plugs are compressed whole hops, but they're not processed into minute particles like pellets are).
Chill Turn off the heat and turn on the water flow through the chiller. Last check that everything is sanitized. When you can hold your hand on the outside of the boiler, you're getting close.
Drop To Fermenter(s) Just as it sounds - let the beer flow to the fermenters and put airlocks on them. Oxygenate if you can. Pitch your yeast and clean everything up.
bob
I went to Lowes for the ball valve & related components last night. I put them together to make sure it would all work, and then went to the checkout counter. The brain surgeon at the cashier station only charged me for the ball valve and braid. I guess sometimes it's good when people are dumb
