When you meet Caeus for the first time, he asks if you will obay him, if you say yes you join the blades , if you do this, does this stop you from joining the other guilds such as the fighters guild for instance??

No, joining the Blades will not prevent you from joining any other guild or faction.

My character is actually member of:
Blades
Assassins (Guildmaster)
Thieves (Guildmaster)
Ashlanders
Fighters (Guildmaster)
I Cult (Guildmaster)
Tribunal (Guildmaster)
I Legion (Guildmaster)
H. Telvanni

The only conflicting factions are Fighters and Thieves, but one can still manage being guildmaster of both if carefull

Obviously spoiler, but since you asked...
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No. I became Fighter's guild guildmaster, I am a mage's guild member, and i could join even the thieves...

Anyway, I don't think you can complete the main quest without becoming a blade.

cheers that want i wanted to know, as i have saved the game before he asked just incase it stopped me joining other guilds.