You're in luck! We went to Costa Rica last year in November (two months ago).
Weather-wise you'll be fine. It is warm and humid, but not uncomfortably so. My wife wore shorts, hiking trousers, regular trousers, and she was fine. We were never cold, and we were never particularly hot unless out in direct sun, which you actually don't see much of... it's just a wonderfully pleasant time to visit. Hotels are very casual, don't worry. Of course, bring a range of clothes.
Bugs... we didn't see any bitey bugs the whole time. Maybe one mosquito, so don't worry. We loaded up on deet and never really needed it. MAYBE only in Monteverde at night, although they say you need it down south.
As for tours and activities, they are all tourist traps! You're talking £30 for two hours walking around someone's back garden for coffee or chocolate tour. The skywalks are a bit samey and again, cost a fortune.
We absolutely recommend night tours! "Tarantula way" with a guide called Chris was amazing. Other night tours were hit and miss, but for actual wildlife, you'll see ten times more at night.m.facebook.com/100069414803584/
If you're driving, ABSOLUTELY get a 4wd!
You'll get so so bored of beans and rice for breakfast, lunch and dinner... so pop into snack shops and load up. You might see the odd Taco Bell or KFC along roads, but that's about it, they're rare.
You're just coming out of turtle egg laying season so look a few of these up.
Hotels LOOK nice in the images from say Hotels.com, but they are all a bit rundown unless you're on the West Coast. Don't expect much here, but there's nothing wrong with them...
Most things are pay in cash and they preferentially go for USD.
You can never hike too much in Costa Rica. Manzanillo was my favourite. If you're going up to the crater, go EARLY!!!-otherwise you'll just see cloud.
Anything else, just ask :)