Mystery Mold: try Hollow Bastion. Land at the Waterway, go though the bubble behind the gate and into the Dungeon. If Fungi appear, immediately open with Stopga, then unleash a Trinity Limit (Critical Plus abilities help a bit too). They may not drop a Mold, but keep trying, you'll get it.
Typhoon blueprint: Typhoons appear between Agrabah & Halloween Town, and they're very tough to take down. What I recommend is loading your ship with 4 Ultima-G's and 6 Meteor-G's, go until the "transition" (when no enemies/obstacles show up), and look on the right (if coming from Agrabah) for a white Typhoon ship (it comes near the end). Decelerate to get some extra time to shoot it down, as it'll take a lot of shots to go down. I also recommend putting on 2 Osmose-G's to scoop up the Blueprint.
Defender: I recommend the 3rd District in Traverse Town here. Equip as many Lucky Strikes as you have, defeat the waves of Defenders and Darkballs, and if the shield doesn't appear, leave towards the First District, enter the Item Shop, then return to the 3rd District to try again (so 3rd District -> 1st District -> item Shop -> 1st District -> 3rd District). This route brings 6 Defenders per run.
Wizard's Relic: The Relic takes a similar approach, but instead of the 3rd District, head to the Alleyway (Alleyway -> Green Room -> Hallway -> Red Room -> Alleyway). This route has 13 Wizards on it, so it's all just a matter of luck here (again, 3 Lucky Strikes for best results)
Sephiroth: there's plenty of strategies you can use against him, but make sure you come in with a full stock of Elixirs on Sora. Having Strike Raid, Dodge Roll, Guard, MP Haste, both MP Rages, any Critical Pluses, a Combo Plus (only one), and Counterattack is a good idea as well. Second Chance is also vital if you get hit with Heartless Angel (which is the big reason for those Elixirs). Otherwise, it all just comes down to hitting him without dying yourself.
Max level: You should probably tackle this first before anything else, and you might get the Relic and Shield while doing this. There are a bunch of places to level up, but I found the fastest way is to cycle through Traverse Town (1st District -> Alleyway -> Green Room -> Hallway -> 2nd District (ground) -> Gizmo Shop -> 2nd District (roof) -> 3rd District -> 1st District). Each time through this route gains a very generous amount of EXP, and each trip only takes about 8 minutes, so it leads to some very fast and pretty easy EXP. Alternatively, you can go around Hollow Bastion in a similar fashion.
Things I learned from Earthbound: Toothbrushes blind people, mushrooms are evil, and trees explode when they die.
I'd recommend getting the weapon drops first, then, if you're not at the maximum level by the time that you finish doing so, just killing Sephiroth repeatedly until you are. I found that to be a really fast way to max out, personally.
For issues with the latter effort, see the Enemy Cards and FAQ sections of my ReCOM walkthrough; been there, done that. Avoid ReCOM's Cheats page, which can tell you to jump through hoops that aren't necessary (like orbiting Mars isn't needed for a lunar landing). Maxing Riku's level is a grind, pure and simple, but exploring all the map cards can make it interesting.
Take this to the ReCOM (or KH2-FM+) board for more chitchat on that game, if you like. Dead boards stay dead only as long as no one posts.
Guides and other contributions: http://www.esque.com/slr/gamefaqs/ FFX, FFXII, KH, KH Re:CoM, KH2, Okage: Shadow King, Secret Agent Clank