As you've discovered that simba will exchange whatever he's got for food, thats the base for training him that parting with something results in a positive reward.
Practice with some really tasty treats, use the same command to get him to 'drop' or 'leave' the item you want and in exchange give him a high pitched 'good dog' and a special treat (a tiny bit of sausage or cheese) - eventually he should give up what he's got expecting a treat, gradually reduce the amount of times he gets a treat in exchange.
No idea re: the cat - have never mixed the two in my household - not because I don't think its possible, just because we've never owner a cat
With waking up early - is it because he needs a wee? If you want a lay in try taking simba for a walk later than usual, and out for his last wee later than usual. My two are programmed to wake up for their wees about 7am. They go down for their last wee at about 10.30pm. If we take them down later at night, they sleep longer in the morning.
Most springers are happy to have their wee then go back to bed

especially if its your bed and you get back with them for snuggles
You're right to be cautious with the agility - most classes won't take a dog until its 18 months - 2 years as its not good for their physical development.
At 14 months most dogs go through a stage of ignoring their owners, you just need to keep on with the training, small amounts every day to reinforce it. Spend evening practicing the basic commands, but use an extra tasty treat as a reward. Most springers bend over backwards for a special food treat
I'm from down south so can't recommend any good trainers - but as you've already been to classes and found simba responded well, why not see if they do a class the next level up.
Good luck