National Park and OTS Access - Most national parks open at 8:00 am. and close at either 4 or 5 pm. and cost 10-20 dollars (usually dollar currency is fine). Many are closed on Mondays. However, Palo Verde and La Selva are official OTS designations and were open on Monday last time I checked. Carara National Park was also open on a Monday on my last visit.
National Parks are serious business. Birding guides are not allowed to enter national parks before their official opening times. They get in real trouble if they are caught. Please don't ask them.
Private refuges and local parks are a bit unpredictable in their hours. You may be able to get in a local park before or after hours, but there are no hard rules about that. Sometimes a booth is unmanned, and there's no one to take an admission fee. I've gone into to several local parks and refuges when there was no one to take my money as an admission fee, then paid on the way out if someone was in the booth. It's never been a problem yet. When in doubt, play it safe and only stay within the appropriate 8-4 time frame. Check ahead if possible.
There's a more peculiar price structure for touring La Selva OTS. Entrance fee structures can be found here.
Weather can be a problem any time of year, so I wouldn't let the summer wet season deter me if I really wanted to bird on my own in summer. The months of May through early August are wetter months but not dramatically wet. We're not talking monsoon season. Usually one gets afternoon or evening rains at that time.
The summer wet season has some definite peculiarities. Seasonal rainfall by month is sometimes quite different in each geographic area of Costa Rica during this season. Many tour companies like to say that there is a "little summer" in July when rainfall is less than it is during the surrounding months of June and August. The tourist industry loves using this factoid. Unfortunately this is not altogether true on the Caribbean side of the country and in southern Costa Rica. Statistical measurements show that July is frequently the wettest month in parts of the Caribbean lowlands and on the Osa Peninsula (although most mornings are generally rain free). Guanacaste and some of the central mountains, on the other hand, do show substantially less rainfall in July than the surrounding summer months of June and August. In essence, I take the "little summer" story with a grain of salt. Avoid making plans in September and October if it can be helped (unless you are exclusively birding the Caribbean coastal areas which are slightly dryer than the rest of Costa Rica during those months). Outside of that, I wouldn't worry about it. The wettest birding vacation I ever took in Costa Rica was actually during the "dry" season. Conversely, I went to the wettest place in Costa Rica during the wettest month of the season for three days and never saw a drop of water after my arrival.
Internet Access - WiFi Internet access in much of Costa Rica is generally available in most hotel lobbies or resort restaurants. Recently we have noticed that most of the better hotels now offer wireless Internet access in the hotel rooms. It's not blazingly fast and is not perfectly reliable every day, but most people with laptops use it successfully and are happy it's available. My perception is that wireless access continues to be upgraded every year.
Span Bridges - Span Bridges are bridges where one is allowed to walk leisurely, sometimes at high elevations through the canopy, and observe wildlife. There are productive span bridges at Monteverde, Arenal, and Heliconias Lodge. These bridges are occasionally very productive for birdwatching. However, bridges like these move a bit when people walk on them. I went to the Arenal Hanging Bridges twice early in the morning with mixed results. People walking on the bridge made birdwatching difficult. It's like trying to bird from a raft in open ocean. I was finally told to bird on the bridges in the afternoon after the tour groups left - around 2:00 PM. This was much better. I like the span bridges a lot in general, but it is really feast or famine. One may need to visit multiple times to reap the benefit. And if it's not completely obvious, span bridges are not zip lines. No sane person birds from a zip line.
Cell Phone Service - Trying to explain cell phone service in Costa Rica hurts my brain just thinking about it. However, the Costa Rica Guide website has a very good summary of the current issues - but even then it's still confusing. All the U.S. providers like ATT and Sprint handle international calling a little differently if you're bringing your cell phone. Discuss it with your provider's customer support for the best answers.
The more devices that can be left at home, the better... in my opinion.
Tipping - Most bills in Costa Rica related to wait-services often include a 10% gratuity in the price of your meal. Check all restaurant bills for this. Nevertheless, I always tip, sometimes generously. I make sure I'm tipping at least 10% on top of the established 10% already taken out.
Bird guides almost always get a good tip. I'm usually at my happiest after a day with a bird guide. For a multi-day tour, I usually tip guides at least $20 a day. For just a single day of guiding, I may tip as much as $20-50 or more depending on how invested the guide is in showing me specific target birds. Sometimes tipping seems never-ending, but I just budget it into cost of the trip. In my opinion, the tipping of guides is an essential part of the natural history tourist industry. Tourism may be big in Costa Rica, but it's seasonal. The guides themselves aren't getting a consistent annual return for their services. Good bird guides are ready to start birding at 5:30 AM, and they sometimes work well into the night with owls. They cart around scopes, field guides, and playback mechanisms. Most of guides I've been with worked long and hard to get people to see birds. I know what most bird guides in Costa Rica charge for their service. Adequate compensation should include a tip.