My trimdown:
1) Eliminate the racial pantheons. If you want 20-30 gods, there's no reason for the elves to have their dozen, the dwarves theirs, etc. I see no reason why goblins couldn't worship Bane as easily as Maglubiyet (they could even *call* him Maglubiyet, and have him look like a gigantic (hob)goblin).
2) Eliminate the Mulhorandi and Untheric pantheons. Well, not eliminate per se; just make the "god-kings" incredibly powerful (im)mortal beings rather than true gods.
3) Then the deities. I'd go with the following:
-Azuth (magic, arcane spellcasters)
-Bane (general LE)
-Bhaal (assassins, necromancers, gibbering death priests)
-Chauntea (farmers, common folk)
-Gond (craft, invention, artisans, tinkers)
-Lathander (sun, light, athletics, general NG)
-Malar (hunters, evil rangers & druids, barbarians)
-Mask (thieves, liars, shadows)
-Mielikki (good rangers & druids, guides, trackers, borderfolk)
-Oghma (knowledge, scribes, bards)
-Selune (moon, general CG)
-Shar (illusion, deception, darkness, liars, plotters, Underdark folk, general NE)
-Silvanus (nature, neutral druids, general N)
-Sune (love, beauty, art)
-Talos (violent aspects of nature, storms, general CE)
-Tempus (war)
-Tyche (luck, general CN)
-Tyr (justice, paladins, rulership, general LG/LN)
-Waukeen (trade)
For a death god, I'd say it depends on your choice of flavor. Either an uncaring, distant, cold deity (Jergal), an evil Grim Reaper-necromancer type (Myrkul), or a just-but-distant, solemn god (Kelemvor).
I suggest this lineup because it provides a balance of aligned deities, reasonably preserves the flavor of the Realms, and gives all character classes and standard archetypes a patron deity of sorts. I left out Mystra, though I think she's actually pretty central to FR, because Azuth seems a bit more of a traditional wizard patron.
I certainly don't think you need many evil deities. In a small pantheon, it's unlikely that there would be many evil deities... certainly not worshiped, anyway. To be honest, it surprises me that the Realms has as many evil deities as it is.