To create "nonstandard combination of Races and Classes" is simple!
Let me share it with you, cause I have just finished it myself too.
You will need to edit the followings:
CharBaseInfo.dbc file
PlayercreateInfo.DB file (in Mysql)
Player_levelstats.DB file (in Mysql)
Player_createinfo_spell.DB (in Mysql)
Player_create_action.DB (in Mysql)
If you edit these , there should not be any problem.
Short description: (Write me privately to explain it step by step if u don't understand something!)
1.CharBaseInfo.DBC determines Races/Class Combos
2.Player_create_info does the same but in Mysql database and you can set different spawn location with the coordinates and the map id.
3. Player_levelstats determines which stat of the nonstandard class should get level by level. If u accept my advice just simply copy the already existing templates so it could be faster.
4. Player_createinfo_spell - this is the point when it gets a bit more complicated.
Your custom new class wont have the basic abilities (racials etc.) it should already have. (Arcane Affinity etc.)
So u have to determine in this DB what to have. But take a good look, cause here you have to use ClassMask and Racemask IDs not Class and Race IDs (so the bit value form - for example : bloodelf which race id is 10 , racemask here is 512!) and if u want to allow for multiple races the same ability/spell or whatever you have sum them!
Don't forget that for example if u create Bloodelf Warrior, like I just did, and u edit player_createinfo_spell to provide Belf Warrior the Arcane Torrent Ability that ability wont give u rage!

(you have to create or edit the spell to provide you rage, cause the Player_createinfo_spell is using different spells for all specific classes related to their source of power.
5. Playercreate_action is just about what spells should be placed out to your actionbars when u log in! (like auto attack, arcane torrent, and 2 class spells i think)
This is not that important just an option but

we are working to get it perfect!
I hope it helped you!
Keep me Updated about your progress!
Trust me, it should take like 1 hour maximum to get these done and working!
ID Value Name
1 1 Human
2 2 Orc
3 4 Dwarf
4 8 Night Elf
5 16 Undead
6 32 Tauren
7 64 Gnome
8 128 Troll
9 256 Goblin (4.x)
10 512 Blood Elf
11 1024 Draenei
12 2048 Fel Orc
13 4096 Naga
14 8192 Broken
15 16384 Skeleton
16 32768 Vrykul
17 65536 Tuskarr
18 131072 Forest Troll
19 262144 Taunka
20 524288 Northrend Skeleton
21 1048576 Ice Troll
22 2097152 Worgen (4.x)
24 8388608 Pandaren Neutral (5.x)
25 16777216 Pandaren Alliance (5.x)
26 33554432 Pandaren Horde (5.x)
ID Value Name
1 1 Warrior
2 2 Paladin
3 4 Hunter
4 8 Rogue
5 16 Priest
6 32 Death Knight (3.x)
7 64 Shaman
8 128 Mage
9 256 Warlock
10 512 Monk (5.x)
11 1024 Druid
12 2048 Demon Hunter (7.x)