Bluejacket casts fittings in a material called britannia metal, which is a mixture of tin, copper, and antimony. It's a light silver color, almost exactly like the old lead alloy that model companies used to use. Britannia, however, is far more durable. Whether it will last forever is hard to say, but it won't flower and disintegrate like lead does. (It also costs about ten times as much as lead. That's one big reason why Bluejacket fittings are on the expensive side.)
As I understand it, lead has just about disappeared from the hobby world these days. Model Shipways uses britannia too, and I think most military miniatures are cast from something similar.
I can't figure out how many blocks it will take to rig a model of the Victory, because the number depends on how much rigging you put on it. The real ship, with sails ready to set, had well over a thousand blocks in her rigging. I don't recommend, though, that anybody breaking into the hobby start out determined to include every single line in the rigging of a ship-of-the-line. My normal suggestion is to figure on including all the standing rigging and those portions of the running rigging that hold the yards in position and make them move. That means the halyards, jeers, lifts, and braces, plus the basic gear for the spanker (topping lifts, peak and throat halyards, boom sheets, and vangs) and perhaps the basic gear for the jibs and staysails (halyards, downhaulers, and jib outhaulers). Most people find that's plenty. When you've reached that point, sit back, take a good look at the model, imbibe liberally of the liquid refreshment of your choice, and ask yourself whether you really want to spend an additional year or so on this particular model or go onto other things.
There's no need to order a complete outfit of blocks at once. My normal practice is to order what I figure will last me for a month or so, and when the stock starts looking depleted order some more.
The number of deadeyes is fairly easy to count accurately. The numbers on your list sound reasonable. Again, though, it isn't necessary to buy all of them at once. If you work at the speed I do, it will take you a month or two to set up the rigging (shrouds, stays, and ratlines) of the lower masts. (If you've never rigged deadeyes before, be aware that there's a steep but fairly short learning curve. The first pair is likely to drive you crazy. By the time you get done with the foremast, you and your fingers will wonder what the fuss was about.)
If I were building that kit (heaven forbid), one of the big problems I'd have to figure out would be how to represent the chainplates. I don't remember much about the kit, but if I recall correctly Heller tells you to make the chainplates out of loops of thread. (I think those loops of thread hanging out of the hull may be the lower links of the chainplates.) I'm inclined to regard that as marginally acceptable on that scale. Making them out of wire links would be quite a project - since every chainplate (on one side of the ship) is a different length. I honestly don't know how I'd do it. In any case, you need to decide how you're going to represent the chainplates before you order the deadeyes. I'm not sure the style with the strops cast integrally would work. The strops may not be long enough to project below the channels.
You might want to order a dozen of each fitting and take a good look at them, before you lay out the cash for the whole outfit.
Bluejacket's "rope-stropped" blocks have grooves around them (which, in practice, need to be cleaned out with a file before they'll work). The "iron-stropped" blocks represent fittings from a later period. They have the strops cast integrally with them. Generally speaking, they aren't appropriate for 1805.
The new Bluejacket catalog shows only one size of turned brass gun: 1 1/2" long, at $2.75 apiece. There are seven different sizes of Britannia metal long guns, ranging in length from 1/2" to 1 7/8" and in price from $1.35 to $2.80 apiece. I've never actually used any Bluejacket guns, but on the basis of the catalog pictures I don't think they're nearly as well detailed or proportioned as the Heller ones. And I don't think the Bluejacket ones are available in all the necessary sizes. And the muzzles would have to be drilled out.
I'm about 99 percent sure that all the Victory's guns were iron. (The British navy had virtually abandoned the bronze/brass gun by the end of the American Revolution.) So the barrels would be black. My recommendation would be to clean up the joints on the Heller guns and paint them black.
You're right: the Longridge book (or one of the McKay ones) is just about essential for this project.
Hope this helps a little. Good luck.