2) Some items are quest specific and otherwise useless, eg the wardstone. I collect them anyway, as memories. Warning: Never ever store items in a stronghold that don't belong to you yet, because it will be completely reset if you get it (spell: all items gone).
3) The lich will probably make short of your summons, which isn't necessarily bad, because otherwise the party would suffer the impact. One important point in fighting liches is to rip their magical defences asap, Breach, Pierce Magic, Ruby Ray etc work good. Another point one is to have someone in the front row who is able to withstand the initial timestop attack (different liches do different things during timestop).
7) Chromatic Orb on high levels far better. It has a saving throw, but it's level 1 and easily rivals higher level spells concerning effects.
About cheesiness and power of summons: Summons are common tools of the wizard. He simply has the choice to summon, buff, blast or whatever. On higher levels, most summons are basically cannon fodder, except for some HLA summons, which can be damn powerful. There are some cheesy variants, like the turned vampire army from intentional wish abuse in combination with an evil cleric, but there are other powerful tactics at those levels as well (the truly murderous ring of / spike trap combo for example).
As long as you don't abuse the engine like especially UserUnfriendly describes it in
The Improved Guide To Cheese and similar posts sophisticated tactics ain't cheese, though maybe powerful.
