The site to which Donnie's referred us appears to me no less than the complete text of George Campbell's The Neophyte Shipmodeler's Jackstay. What a find! The original was published back in the 1950s by Model Shipways; it was intended as a guide for building that company's solid-hull wood kits. That being the case, some of the techniques in it are dated (such things as styrene sheet, acrylic hobby paints, and CA adhesives didn't exist in those days) and of limited value to plastic kit builders. But the information about the construction and evolution of ships - especially rigging - is just as valid as ever. My suggestion to any newcomer: print out the whole thing and study it till you're cross-eyed. If you learn everything in that book you'll have made a big step toward becoming a knowledgeable ship modeler.
Regarding Bluejacket blocks - the website is www.bluejacketinc.com . The question to the question about block and deadeye sizes, unfortunately, is hard to answer. I suspect the deadeyes in the Heller kit are about the right size; if you match them with Bluejacket parts you'll be on the right track. The number and sizes of blocks will vary according to a number of factors. Several decisions need to be made in rigging a ship model. The rigging of a real seventeenth-century ship-of-the-line, ready for sea, would include well over a thousand blocks in over a dozen different sizes. When you start reading up on how rigging works, though, you'll see that a lot of those lines are optional. Many modelers start out with the basic running rigging - lifts, halyards, and braces on the square sails, and some of the basic gear attached to the lateen mizzen yard. That's the gear that's necessary to keep the spars lined up, and what would be seen on a ship that had been at anchor or tied up to a pier for some time. The sails require a huge number of additional lines - sheets, tacks, clewlines, leechlines, buntlines, bowlines, etc., etc. How much of that gear to include on a model is really up to the original modeler.
In any case, to rig a model like that requires lots of blocks in lots of sizes. If I remember correctly (caveat: there's a good chance that I don't) even the smallest blocks in the Heller kit are on the large side. My suggestion: (1) Don't worry about blocks at all for several months. You're a long way from needing them. (2) When the time does come, read up on the subject (the Anderson book gives a good idea of how to figure out block sizes) and order a dozen each of several sizes. Bluejacket gives good mail order service; waiting for merchandise won't slow you down much. (3) Figure out how much rigging you really want to put on the model (you can always add more later), make up a list of the blocks you'll need, add 5% or 10% to cover emergencies (e.g., block-eating carpets), and order as many as you think you'll use up in a month or so. A complete outfit of deadeyes and blocks for a model like that will cost several hundred dollars, but there's no reason whatever to spend it all at once.
The golden rule about rigging line also applies to blocks: if in doubt as to size, err on the small side.
Regarding parrels - the answer to the question becomes obvious when you realize that a yard, in addition to swinging around the mast (to receive the wind), has to slide up and down the mast. It's a point that lots of newcomers miss - but a crucial one. In a typical seventeenth-century ship, the lower yards are the only ones that stay at the same height all the time. (In later centuries the lowest yard on each mast was fixed in position vertically more-or-less permanently. The lower yards in most seventeenth-century vessels had parrels like the upper ones, but the lower yards would normally be kept in their raised positions unless the topmasts were struck.) The topsail and topgallant yards move up and down when the sails are set and furled. To look right in the eyes of a knowledgeable observer, the yards of a model should only be in the raised positions if the sails are set. The parrel assembly is fastened to the yard, providing the means by which, with a mimimum of friction, the yard can swing around the mast and slide up and down it.
You can get the idea from the photos of the kit in one of your earlier posts in this thread. In the boxtop painting the sails are furled and the yards are lowered. In the side view drawing on the cover of the instruction booklet, visible in the second photo, the sails are set and the yards are raised.
Regarding sails - few subjects are more likely to start an argument among ship modelers. I personally happen to agree with Donnie: I like the look of a model with furled sails. We've had a good, ongoing discussion of the subject here in the Forum; here's the link: http://www.finescale.com/FSM/CS/forums/350911/ShowPost.aspx
That thread contains quite a few thoughts on the pros and cons of set sails, furled sails, and no sails; please take everybody's opinions in the context of everybody else's. I will say this much, though. Ship modelers don't agree about many things, but the one that may get the least argument is: vac-formed plastic sails, by definition, look like h![Censored [censored]](/FSM/CS/emoticons/icon_smile_censored.gif)
l. I don't think I've ever encountered anybody who didn't think those things belonged in the trash. Beyond that, there's plenty of room for discussion and personal taste. My suggestion is to think about it over the next few months. You' won't need to make any decisions about sails for quite a while.