@RP: Perhaps, but I don't need STAB. If that were so, what would I need two other attacks for? It's all in type coverage. STAB isn't always required. You need to pay more attention to covering EVs, IVs, Natures, Base Stats, and actually applying the most beneficial moves to a Pokemon to suit its environment. In all honesty, unless I come to a neutral Pokemon, I never worry about STAB or not. Yes, it's important, but when you weigh in all of the other factors, all else is more important.
IMO STAB is important, and since many of the pkmn on my team have fairly good defence the attacks you use will not have as much effect as you hope. Furthermore, if you use attacks that do not reflect your pkmn's type, I can as well, and I can fight back against your attacks.
Ah, I see.
Yes, you can get Leafeon pre-Elite Four.

Not in Diamond or Pearl (in-game only, anyway), but in Platinum, you can.
If I might make a slight suggestion, you would
much rather prefer to have an Infernape over a Rapidash. Trust me, you'll be better off for it. And Floatzel and Gastrodon also work as really good substitutes for Empoleon. Just my two cents.
I start with Empoleon, and as you said, importing from another game wold take away much of the fun, therefor I can't have Empoleon and Infernape. Also, Infernape is weak against flying, and psychic, which rapidash is not weak against. I like Floatzel, but I find it not quite as good as Empoleon, plus Empoleon gives me a steel type which can't be poisoned. Gastrodon is slow and I don't like it.
Special Walls, not blockers.

Blocker isn't a competitive term, but I guess I'm getting too technical here. Anyway, the whole point of Blissey is to act as a buffeter for the team. Its normal purpose is to hold off Pokemon that focus on Special Attack. It also focuses on reinforcing and strengthening the team, which is why it has moves to use such as Aromatherapy. And if a Physical Sweeper such as Lucario showed up, all you would have to do is switch out before it can do anything. (although you would have to be cautious of Pursuit)
Whatever the name may be, it does the same thing... And switching out can be done on any pkmn...
Well, it depends. If I'm preparing a competitive Pokemon, then yes, I breed for a specific Nature. While some people think that its smart to always go with a Neutral Nature, that's actually a very big mistake. Say, for example, I use a Special Sweeper. Why, then, do I not use a Nature that can lower my Attack in return for raising my Special Attack? The Attack stat won't be used anyway, and you can always afford to have a 10% bonus in a stat that is crucial to a Pokemon, so all competitive Pokemon should have a focused stat. For example, I have a Gallade and an Electivire that I use for competitive purposes, both of whom are Physical Sweepers. My Gallade, on one hand, has a Jolly Nature, which lowers his Special Attack in return for raising his Speed. I'm not going to be using his Special Attack, and I can really use an uped Speed stat on Gallade, so I should pick an appropriate Nature for him to suit that. Also, I have my Electivire with an Adamant Nature. Adamant Nature increases Attack at the cost of Special Attack. I think that one should explain itself.
As for my normal, in-game team, I try not to worry about it, unless it absolutely hinders the Pokemon's purpose. For example, I have two Pokemon on my team (Luxio and Monferno) who have Neutral Natures. Surprisingly, on the first time, without actually thinking about it, it turns out that my Grotle got a good Nature, Adamant (+ATK,-SATK) to be exact. However, I finally caught a Gligar last night, but I realized that it had a Bold Nature (+DEF,-ATK). Defense is Gligar's/Gliscor's best stat, and I need focus to be put on Attack. Thus, I can't accept Bold for a Nature. Overall, though, while I do worry about Nature, when it comes to in-game Pokemon, I tend to not worry about it.
Cool. I'm not in to the game that way. I train my pkmn wherever and however and they turn out to be pretty good.
My team will be:
Tyranitar
Dragonite
Metagross
Empoleon
Leafeon
and a lightning type, either Raichu or Manectric
I can have an Ursaring w/ Avalanche and Earthquake. You don't have a Fighting Pokemon on your team, and since Ursaring has a base of 130 Attack, your team is in big trouble.
Ursaring is not an ice type or ground type... saying that I don't have a fighting pkmn on my team means nothing and you pointed that out yourself by putting two moves that are not the same type as your pkmn in the post. I think that answers back to you pretty well.
Anywho, how about this team:
Dragonite (Drgn/Flng)
Tyranitar (Rck/Drk)
Togekiss (Nrml/Flng)
Leafeon (Grs)
Ampharos (Lghtng)
Toxicroak (Fghtng/Psn)
Yes, there is no fire or water, but I can give fire and water moves to others...