I'll be playinbg the Chicago Grand Tournament next weekend and I find myself so excited that I often sit in bed and wonder what types of armies I'll wind up playing. After finally revising my army to be much more competitive than its original form, I just need to think about how I'm going to beat my opponents on the board.

Here's a quick run down without wargear or squad sizes:
i've got a mostly foot slogging force bearing storm bolters and lots of faith(2x sisters, 1x Celestians). Also a repentia squad, two flying Canonnesses (one with evis, one with BW), dominions with meltas in a flamer Immy, 6 seraphim (VSS evis and 1x inferno), Retributors with 4 heavy bolters and of course two exorcists.

Here are the armies I'm worried about fighting:

Static Chaos
Eldar Skimmers
Tau in general

If anyone has something that can ease my mind about how to prepare myself for fighting unknown enemies at a competition, especially against the abovementioned forces, let me know!