OK, I'll try to answer each post as I go.
I'll explain the way I do it, and then make my recommendation for how YOU should do it.
I normally start with a stack of 35-45 layers of 1080/15N20 in 1 1/2" wide X 6" long. Since nickel oxidizes more and faster than straight carbon steel, I build the initial billet with 1080 on the outsides. Since the 15N20 is thinner, if it is placed on the outside, it not only will oxide up quickly, but will sometimes "bow" in the middle, which can create a void in the billet. I MIG weld a line across the front edge on both sides of the billet, another across the center of the edge sides, and then weld on a piece of scrap rebar as a handle. FOR YOU, doing it by hand, I would recommend going with about 10-12 layers of 1" wide stock, because that is about the most that can be effectively worked by hand.
I then place the billet in the forge (the forge has been preheated to approx. 2350F before I ever place the billet in it). I let the ENTIRE billet come up to a bright orange, then flux it fairly heavily with anhydrous borax on both of the "edge" sides. I usually hold the billet and roll it around until the flux flows and covers the entire billet. I also try to let most of the excess flux drain off in a pan next to my flux box, just to keep as much as possible out of the bottom of the forge.
Back into the forge, and allow it to heat until the flux is "sizzling" like water in a hot skillet. Another indicator is that when you take the billet out of the forge, it will be "fuming".
Welding heat is generally that point where the surfaces of the steel become "semi-molten" and in many ways act like hot plastic. A forge weld can occur simply by having two pieces of steel touching inside the forge, and when the correct temp is reached, the surfaces that have become semi-molten will "join". Keeping that in mind, when you bring the steel to the anvil, start with LIGHT blows....basically tapping with the hammer. The steel will feel "mushy" and as the surfaces of the steel join and it beings to slightly cool, you will feel the steel "stiffen" under the hammer. As the steel begins to stiffen, you can exert more powerful blows. DO NOT HIT THE BILLET HARD WHEN WELDING! Most often if your blows are too heavy, you will either "squash" out the semi-molten material on the surfaces, or the pieces will want to "slide" past each other. Either of these will result in a non-welded situation.
Doing it by hand, I would recommend choosing the end of the billet closest to the handle, and work towards the other end from there (working away from yourself). This will "squeeze" the excess flux and "junk" out the end opposite you, and help prevent you from being splattered with molten flux.
It may require several welding heats to work the entire billet by hand.
Once the welds are completed, the next step is to draw out the billet.
The reason that many of us use power hammers and presses is to simply quicken the overall process, but more so it's to reduce the number of times we expose the steel to the extreme heat required to weld. For example my billet of say 35 layers, will draw out to approx 35-36" long. I let it cool a bit, then grind both sides COMPLETELY clean with an angle grinder. Then I divide it into as many equal length pieces as I need to achieve the total layer count I desire. In this case, let's say I want 350 layers. I take that 35" long billet, that has been ground clean on both sides and cut it into 3 1/2" pieces, which yields me 10 pieces. I re-stack those pieces, and forge weld, and I have a billet that contains 350 layers. From there its a matter of manipulating the billets to achieve the specific pattern I desire, or forge it to a usable size if I want to forge random pattern blades from it.
YOU, doing it by hand with a 10-12 layer billet will have to draw that billet out as long as you can while keeping it approx 1/4-5/16" thick. Your billet will be much shorter than mine, likely around 12-15". Let's say it comes out to 15"....you then want to grind both sides clean, and cut it into as many equal length pieces as possible. In this case, let's just say you want 3" pieces....that would give you 5, 3" pieces, which when re-stacked would make a total of 50 layers in the billet. If you wanted 300 layers, you would have to stretch it out again, and cut into at least 6 pieces and re-stack/ forge weld again to achieve that 300 layers.
Can it be done by hand? Certainly! My first several damscus blades were all done by hand. It was a LOT of work, and it took several weeks of time, but I did it. Not long after is when I started searching for my first power hammer!
A few notes that I think are vital:
1. The fewer times you expose the steel to welding heat, the better it is for the steel. Extended duration at high heat will cause grain growth, and carbon migration/element segregation. This will result in a weak blade, and is often visible when a damascus blade is etched, and that etch has a "muddy" appearance.
2. I feel it is critical to success to completely clean both side of a billet, then cut and re-stack rather than "folding". In my experience folding a billet results in about a 50% success ratio, where as grinding both side of a billet clean, then cutting and restacking result in about a 95% success ratio.
3. When using an angle grinder to clean off a billet prior to cutting and re-stacking: ensure the grind marks run ACROSS the faces of the bar (cross ways, from edge to edge). This induces a capillary action, creating a way for excess flux and crud to exit the billet as you forge it. I've experimented and found that if the grind marks run lengthwise on a billet, it will almost always create a flux inclusion.
4. Although your instinct and common sense would tell you to "Beat the Crap outta it" when forge welding, just the opposite it true. Minimal force is required to forge weld....in fact if too much force is used, the chances are good that the pieces will not weld. The necessity for power comes in AFTER the weld is made, to draw out the billet.
5. Although you may hear differently, things such as cable and chain are some of the most difficult materials to forge weld....in cable you have a bunch of tiny round rods (wires), loosely twisted together, that try to slide past each other when attempting to weld them. Chain has many different alloys, some that are very incompatible with each other, and there is a great deal of "air space" in these materials that must be closed before things can "weld". Flat bar is by far the simplest and easiest to successfully weld. I think the main reason that some will suggest cable or chain over flat bar is because with those materials, there isn't as much drawing and re-stacking necessary to achieve a pattern.
6. It's all about learning! The more you forge weld, the better at it you become, the more experience you acquire, and the "easier" it becomes.