In general, the weather at San Isidro Lodge is a lot less predictable than in many other areas in Ecuador. The weather has relatively wet periods during the 'dry' season (September-January), as well as dry periods during the 'wet' season (February-August).
The currency in Ecuador is the US dollar (so no need to worry about changing cash if coming from the US). As a general hint for traveling in Ecuador, it is better to bring bill denominations no larger than $20 since larger bills are often not accepted.