First congrats on the Mitts . those can be abitch .
Second i am glad you are choosing not to AFB your way to 75 . this causes alot of problems not only for you but also for those you encounter .
Avatars :
Primes are the way to go . the Main reasons you want primes instead of Lv20 Mini are these ; First and foremost its ALOT easier . I'm all one for a challenge but srsly the Mini fight is not to be taken lightly . one mistake and you're toast . Second is gil whoring . As stated by other posters a SMN75 can pretty much Solo all the primes but Diab and Fen . Garuda and Levi can end in Stalemate because of Whispering Wind/ Spring Water spam , but all being said you can make an easy 40K with out all the running by using the Minifork Warp . just need to get to the NPC which is pretty easy . This is also stated but might as well over state it . Fenrir can be handled by 3 SMN75 who know what they are doin . i havent ever seen it done by 2 but i suppose it could be possible . Most SMNs for some reason are kinda scared of Diabolos , but rest assured he can be defeated w/o 5 BLMs .
As far as EXPing goes you have a few options . If you choose to seek be prepared to be the last one asked to join a PT and be the main healer . This aspect of the job is kinda hard til 22 when you FINALLY get cure2 (WHM sub of course) but it will never be truely easy . SInce you have Mitts and i presume a Light staff Main healing will become easier (providing the PT has a refresh ) by utilizing Healing Ruby and later on Healing Ruby 2 . For the MP they use and the HP recovered they are incredible and allow you do the job with lest Cure Spamming . The down side of course is having to keep the little blue guy out all the time . You'll come to find that a NIN tank is your best friend in these PTs .
The other less travelled road is that of Solo/Lo Lv SMN burning . Yes SMN can burn below 65 . And not just off bombs , tho they are the best target . Goblins come in a close second but take a little more research in order to be on par with bombs . Dont forget Gobbies blow them selves up too . You can Solo Bomb popping @ 51 in Ifrit's cauldron but its a CHALLENGE . it gets easier solo @ 55 or so . you can PT there with other SMNs @51 and take it easily to 60 then you can move to Ulegardwatever Range and pop Snolls instead . Ulegard can actually take you to 75 (Agoolki or w/e its called cons as T-VT @ 75) but srsly with AU theres no reason . @ 65 you can start makin SMN burns and take on Mobs that normal EXP PT would fight . a good Camp for 65-68 is Mt Zylom . the Fire Crawlers go down from 4-6 Eclipse Bites . 68+ you can SMN burn Imps .
If you're feeling adventureous and dont wish to follow the crowd with AFBing there isnt much you cant kill . As long as it doesnt heal it self and you can manage your MP , you can grant it a slow painful death at the claws of Carby . MP managment is what makes or breaks you with SMN . It gets Easier @ 20 with the Mitts , then again @ 51 with Staff . If you have or are thinking of investing in a Vermy to use in place of YYR i would HIGHLY suggest ponying up the Gilz and get yourself a HQ Light Staff . the -3 Perp will give you a 1 MP Refresh Carby (like the big dawgs) all the way til Evo Ring @71 . if you dont have a HQ Staff , a Vermy becomes an Austere's Robe with out the -BP timer (with an avatar out of course) .
one last thing , @ 71+ you may want to consider going to KRT and battling the Spartoi skeletons , particularly the Mages . they have fewer HPs , Titan/Shiva/Ramuh own them , and they Drop Blizzaga 3 wich i am sure is 150k+ .
GL . have patience . have fun .