It really depends on where you are located but mostly games are only held at legal fields, not abandoned facilities or anything. In any given year there is probably a big game every month if you are willing to drive a few hours. Border Wars 3 is coming up in the Barrie area I believe, the Quick Pass series in Rawdon Quebec north of Montreal, there is a huge 400+ player game at Fort Drum in New York state in two months, and several others. You can generally play a game every weekend within a 1-2 hour drive of Toronto; some will be very small and others will be average sized games (20-40 people.) You can also sometimes play when under 18 but usually need a parent present. Its not a matter of insurance like with paintball, because there is no such thing as airsoft insurance, but its a matter of legal liability of the property owner.
The fact that you play tactical paintball is a big plug, means you are leaps and bounds ahead of most airsoft newbies. To start in airsoft its probably cheapest and easiest to rent first. Many fields offer rental guns and even those that don't often have players attending that will rent guns to new people. If you are looking to buy there are many options to choose from depending on what type of gun you are after. Being tactically inclined would make me think you would go for an M4/16 or MP5 variant, the two most common types. There are many cheap Chinese brands such as Jing Gong, Echo1, KART, AGM, and many more that have guns that run ~$400 new in Canada but they are known to have a high failure rate. A good solid reliable gun will run you closer to $600-800 plus mags, batteries, BB's, BDU's (which you probably already have), and other accessories. A solid starting budget for outdoor games is around $1000-1500 but can be had for around $600 if you get a Chinese clone gun (but might need a gun doc to work on it sooner than another more expensive gun.) If you plan on playing indoor games to start Toronto has TTAC run by Brian McsomethingthatIcan'tspell and he offers rentals at a low price as well with just a pistol you can play competitively, maybe $250-400 starting budget.
Another thing is it is not important to join a team. Lots of new people think you need to be part of a team to play but you can sign up for any game without being part of a team. When new its actually sometimes negative to join a team right away as you are always lumped with the same people. Being independent and new means you can run with anyone and learn from a much larger experience base.