jesus christ, all those secondaries, how horrifying.
Aight, since I'm fatefag, here is quick guide how to fate.
1. Get Fate/Stay night Visual Novel, read it. It has 3 routes, to finish all of them you need at least 70 hours, if you want to get 100% and all endings, it's up to 90h, maybe more.
2. Watch Fate/Zero anime or read Fate/Zero Light Novel (anime leaves some stuff but translation of novel is so so, your choice)
That's bare minimum.
DO NOT WATCH FATE/STAY NIGHT ANIME BY DEEN, IT'S ELDRITCH ABNOMINATION.
Fate/Stay Night UBW movie by DEEN is equally terrible, watch it only if you want but after reading visual novel. It's better to wait for Ufotable's version.

If you like those, you may want to check out:
- Fate/hollow ataraxia Visual Novel (happens 6 months after F/SN)
- Fate/Extra PSP game (alternative timeline)
- Fate/Apocrypha, light novel, ongoing
- Fate/Prototype preview (15 minute-long OVA, original idea about the series)
There are some other side materials but I don't want to spoonfeed you too much.

If you like the world and concepts about it (nasuverse), you may want to check:
- Tsukihime Visual Novel (stay away from anime, it's terrible)
- Kara no Kyoukai OVA series (9 movies iirc, from 50minutes to 2 hours long)
- Melty Blood PC game
- If you are familiar with nasuverse, Carnival Phantasm anime

And again, there is more but you gotta dig yourself.