Well, first of all if you want to get through the game I recommend something other than Te
The best bit about Fedhas is the part between getting * piety and Lair. You pray over corpses, mushrooms grow, and you can turn these mushrooms into wandering mushrooms which deal a crapton of damage (for that stage in the game) and confuse monsters upon hitting them. I recommend having about 2-3 following you at all times. Lure monsters into mushrooms and kill the confused monsters (if the mushrooms didn't do it themselves).
Inside the Lair and beyond mushrooms are still going to be very useful, but you can't count on them to do all the work themselves.
Oklobs can take out the Zot:5 vault by themselves if you feel inclined to use them that way (and find enough fruit), but I don't like the strategy of saving all fruit for Zot:5. Zot:5 isn't harder than a lot of other places in the game and you shouldn't feel bad about using oklobs when appropriate. Using them is quite simple, grow plants (1 fruit -> 1 plant, rain can also grow plants), evolve plants into oklobs (1 fruit -> 1 plant turned into oklob) and let them do their Thing. Adjust number of oklobs to strength of enemies.
Sunlight isn't great or anything. It just vaporises water when you need it, which can be useful if you don't have a source of flight, and improves accuracy when you attack a glowing monster. Rain is kinda useful to prevent monsters from getting towards you (you can build a moat around you with repeated uses) and is, of course, much better on characters with a way to attack monsters stuck outside the moat. Deep water can drown some monsters.
The growth ability could, in theory, be used defensively, but you should try to save your fruits to grow oklobs and use other means of escape than growing plants and running away.
I think a lot of people overrate his usefulness for a ranged character compared to a melee character. Of course some abilities are better for devoted ranged characters, but his best abilities, mushrooms and oklobs, are great for both. So do what you want when it comes to character selection. Fedhas is definitely a god you can pick for an easy win, it's not a challenge run by any means (mostly due to early mushrooms).