Dear James,
Just figured I'd chime in with some epic-level suggestions.
First off, U_K is usually quite on the ball with his suggestions (in addition to being quite the diligent epic/deity-level system tinkerer!). Do give him a listen!
Now as to the specifics:
Epic-level campaigns are much, much different when you start at epic levels than when you build PCs up from low levels. For one thing, you should establish what kind of game you and your players want. Is it a role-play intensive thing where epic levels are important because they allow for world-spanning plots and challenges? A power-gaming paradise that permits players to indulge in their wildest fantasies of blowing things up and dealing 300+ hp damage on full attacks? A geek's excuse to test the epic-level mechanics? It's important to establish which type of game is desired, because it'll dramatically influence both the kind of game that you're going to be expected to put on for your players, and the kinds of PCs they'll build.
Second, keep in mind that epic-level challenges are highly dependent upon PC build strength. This is even more true at epic levels than of 3e in general. A less min-maxed party will get wiped out in a bare few rounds by a challenge which would be a walkover for min-maxed PCs. Take a long, hard look at your party and decide what level you effectively consider them to be for purposes of matching CR/EL. The monsters in the ELH are particularly problematic in this regard; their CRs generally are pegged to a seriously min-maxed party. (A CR 25 monster in a book other than the ELH is extremely lacking compared to, say, a gloom.)
Third, decide carefully what is and what isn't allowed in your game before starting character generation. There are lots of things to watch out for, including:
1) Broken rules: The spelldancer infinite loop, circle magic, simulacrum, polymorph any object, polymorphing into templated creatures (particularly paragon and pseudonatural beings), the ur-priest, and various other rules holes can be hugely problematic at epic levels. Make sure your players know what is and isn't allowed. Especially important when it comes to epic spellcasting. as written, epic spellcasting can be abused by the munchkin to develop cheap ways in which to add gigantic boosts to ability scores, AC, attacks, and weapon enhancement bonuses, and to do incredibly system-breaking things like using the Transform seed to turn into a paragon ghost beholder or force dragon. This can really ruin your day unless you rely on the simple rule contained at the beginning of the epic spells section: All epic spells must be approved by the DM.
2) Custom item creation. Make sure you vet all non-standard (DMG) items created by PCs or "purchased" by them during character generation. 'Nuff said.
Fourth, planning adventures: Keep in mind that epic-level adventures tend to resemble The Authority or Justice League more than they do LotR. Teleportation, infallible divinations, instant healing, and six-second combats are ubiquitous. Plan accordingly; unless you install specific conditions that nullify teleportation and divination, the party will always be able to find and reach any place they need to (one reason why epic adventures so frequently are set on other planes). Also, death is not nearly so big a deal at these levels; as the ELH says, it's usually just a 10-minute time-out thanks to true resurrection.
As for the Bloodstone adventures: I think that they're a fine choice, but will obviously need to be seriously boosted to accomodate epic-level PCs. At what level did you plan to start your PCs?
I've run a party through these modules, and we had an awfully good time. I made some major alterations, though. Here are a few.
SPOILERS FOLLOW
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H1: At these levels, the bandit army is a relatively meaningless fighting force; the real challenges are Knellict and Banak. I had my PCs capture some spies to learn the location and some minor details of the bandit camp, launch an improved invisible/mind blanked/flying stealth mission into the camp, and meet with the leaders of the army and their summoned fiends and undead in a mighty battle. Upon the PCs' victory, the bandit army was scattered to the winds, easy prey for mopping up by a PC-led militia.
If you're using epic-level (say, 21st) PCs, the bandit army leaders need serious beefing up; one suggestion might be to use the NPCs in the "Razing of Redshore" epic adventure in Dungeon 93.
Also, I suggest a more Faerunian flavor to the names of NPCs and locations: Flip open the FRCS and read the names and language pages, and do a little renaming. Trust me, the very flavor of your campaign will change. Also read FR11 Dwarves Deep and apply a few details therein to the Orothiar and Hilsafar clans. I assume you have FR9 The Bloodstone Lands? If not, I'd suggest grabbing the ESD, reading it through, and applying some backwards continuity to your setting (FR9 is set immediately following the war).
H2: This one can be run as is, although the power of all adversaries will need a SERIOUS boost to meet the PCs' power levels. Fortunately, this is an easy thing to do, given 3e's method for adding class levels to monsters.
As for Orcus arriving: Well, the entire point is that if he shows up, the PCs have lost! If they screw up, they should be spanked just as they deserve for failing to stop the summoning.
H3: Well, it's a bunch of battles. Hopefully, Malhavoc Press will have released Cry Havoc!; it may be worth purchasing simply to have workable 3e mechanics for this series of mass combats. You'll probably need higher-level NPCs on the other side to make sure the PCs have a challenge; I might include a polymorphed fiend or two (the kelvezu from MM2 makes a nice option) to even the odds.
Also, the Assassin's Run is a surprisingly weak challenge, with the exception of having the Grandfather running around ; I'd drop in some high-level assassins with rings of blinking and those nice epic poisons featured in the BoVD Epic Insights web column to shake things up a bit.
H4: This module needs to be seriously retooled, as U_K suggested. Most elements aren't actually that bad; upgrade Arctigis to a great white wyrm, Zhengyi can probably stay at 30th level, and Klavikus needs to be very substantially advanced. Some of the random encounters could be upgraded; the higher-CR undead from MM2 or FF are potentially OK choices, given that Orcus is involved.
I'd also skip the silly St. Sollars crap and force the PCs to use their magic (and brains!) to figure out where they need to go. As for the actual mission: Well, they should be able to use a plane shift or similar spell to reach Orcus's layer directly, or a find the path to discern the correct portal location, meaning that most of the text on other Abyssal layers is probably unnecessary. As for Orcus's layer: Have the PCs sneak into the fortress, brave the traps, and grab the wand, as suggested in the module. Make it pretty clear that powerful as they are, taking on Orcus directly is tantamount to suicide. I'd assume that the removal of the wand cripples Orcus's army sufficiently that the actual destruction of the artifact isn't required. The PCs then are stuck with the Demon Prince's wand, and must decide whether to pursue its destruction or stay on the run, forever fearful of subjecting themselves and their loved ones to Orcus's enmity. (A great epic-level plot hook if I ever heard one!) Hand-walking them to Tiamat's lair and having them kill her (sheesh!) is just too silly, IMHO.
