You have to visit the studio to get a sense of how comfortable it will be for you. You will be spending much time and money in pursuit of getting your music recorded in the best possible way, so you need to feel comfortable in the atmosphere and in the relationship with the engineer. Otherwise you may not be able to realize your potential. Musicians in general are not very good business people. And using a studio is part business. Keep the biz part separate from the art part and sessions will go easier.
Make sure you discuss rates, type of payment, when payment is expected etc. Ask a lot of questions. Most of the time it’s not necessary to do an actual contract, if you like the studio but are getting weird vibes on the biz side of the equation a contract might be called for. Any studio owner will not have a problem with a simple contract that spells out rates, payment, times, options. When talking to the engineer, ask about other projects they have done. What approach they may have on your project. What you as the artist expect for your recording.
Remember, this should be a rewarding experience full of hard work and some pleasant surprises.