[AT&T Samsung Galaxy S II Skyrocket SGH-I727] m4570d0n:
Your problem is, in part, that you used the jb branch for /device/samsung/hercules. You'll need to use CM's cm-10.1 branch for that. Also, you'll have to edit /vendor/slim to add the hercules to the builds.

In vendor/slim/vendorsetup.sh add this line:

add_lunch_combo slim_hercules-userdebug

Pretty sure that is why it's complaining that it can't find /device/samsung/hercules/slim.mk

Also, in/device/samsung/hercules make a copy of the cm.mk file and rename it slim.mk. In that file, change the 3 vendor/cm references to vendr/slim and add the other lines from the slim.mk for hercules jb branch. So instead of this:

$(call inherit-product, device/samsung/hercules/full_hercules.mk)

# Inherit some common CM stuff.
$(call inherit-product, vendor/[COLOR=#ff0000]cm[/COLOR]/config/gsm.mk)

# Enhanced NFC
$(call inherit-product, vendor/[COLOR=#ff0000]cm[/COLOR]/config/nfc_enhanced.mk)

# Inherit some common CM stuff.
$(call inherit-product, vendor/[COLOR=#ff0000]cm[/COLOR]/config/common_full_phone.mk)

PRODUCT_BUILD_PROP_OVERRIDES += PRODUCT_NAME=SGH-T989 TARGET_DEVICE=SGH-T989 BUILD_FINGERPRINT="samsung/SGH-T989/SGH-T989:4.0.4/IMM76D/UVLI4:user/release-keys" PRIVATE_BUILD_DESC="SGH-T989-user 4.0.4 IMM76D UVLI4 release-keys"

TARGET_BOOTANIMATION_NAME := 480

PRODUCT_NAME := [COLOR=#ff0000]cm[/COLOR]_hercules
PRODUCT_DEVICE := hercules

you have this:

$(call inherit-product, device/samsung/hercules/full_hercules.mk)

# Release name
PRODUCT_RELEASE_NAME := T989

# Preload bootanimation
TARGET_BOOTANIMATION_PRELOAD := true

# Inherit some common slim stuff.
$(call inherit-product, vendor/[COLOR=#0000ff]slim[/COLOR]/config/gsm.mk)

# Enhanced NFC
$(call inherit-product, vendor/[COLOR=#0000ff]slim[/COLOR]/config/nfc_enhanced.mk)

# Inherit some common CM stuff.
$(call inherit-product, vendor/[COLOR=#0000ff]slim[/COLOR]/config/common_full_phone.mk)

[COLOR=#0000ff]# Inherit device settings
$(call inherit-product, vendor/slim/config/common_sgs.mk)

#copy boot animation
PRODUCT_COPY_FILES += \
vendor/slim/prebuilt/hdpi/bootanimation.zip:system/media/bootanimation.zip

#copy 00check
PRODUCT_COPY_FILES += \
vendor/slim/prebuilt/common/etc/init.d/00check:system/etc/init.d/00check[/COLOR]

PRODUCT_BUILD_PROP_OVERRIDES += PRODUCT_NAME=SGH-T989 TARGET_DEVICE=SGH-T989 BUILD_FINGERPRINT="samsung/SGH-T989/SGH-T989:4.0.4/IMM76D/UVLI4:user/release-keys" PRIVATE_BUILD_DESC="SGH-T989-user 4.0.4 IMM76D UVLI4 release-keys"

[COLOR=blue]#TARGET_BOOTANIMATION_NAME := vertical-800x1280[/COLOR]

PRODUCT_NAME := [COLOR=blue]slim[/COLOR]_hercules
PRODUCT_DEVICE := hercules

I'm not sure whether that TARGET_BOOTANIMATION_NAME := 800x1280 part is necessary, but that's what it was in the jb branch for hercules. That's not our screen dimension though, as we have a 480x800 display. Actually, I'm pretty sure that line is not necessary and was based on an old boot animation setup in CM on CM9/early CM10 and it can be omitted.

Also, to you and to BMP7777, check the frameworks/opt/telephony package for Slim and add this change if it's not there already:

Qualcomm LTE RILs: do not make mLteRsrp negative (Merged)

edit: never mind, that was added to Slim on the 8th.