Right now I seem to be playing as a speedy dexterity based build with weapons like the Halberd and great scythe:

Halberd +7 Great scythe: Fire ascension

How would you compare the scythe to the halberd? I really like both but the scythe seems a bit slower to me but has better slash attacks and I feel a lot speedier and agile with it, but the Halberd has a quick poke attack and a greater damage output because I upgraded it more.

Here are my current plans of action:

Upgrade dexterity to level 40 for greater base damage output on my dex weapons (currently 16)

Upgrade Halberd to +15 and apply gold pine resin when needed (Should I just upgrade it to lightning instead?)

Make a lightning Uchigatana for bosses where I need quick slashes over slow poke attacks. (My uchigatana is +5 at the moment)

So what do you guys suggest I do? Any pro tips? Is +15 better than fire/chaos or lightning? Halberd vs Great scythe?

I suggest you visit http://www.gamesas.com/topic/1476682-dark-souls-discussion-thread-26/ and ask there.

To give a quick answer... a +15 is almost always better than a Lightning or Fire weapon, especially for just playing the game. (they are more useful for PvP)

Yes, let's continue there.