What can I expect in the future as far as seasons go?
Expect another season about a month or two after worlds.
Is there ever a lul in ranked where you must play normals only?
No, only if the ranked servers are down is there ever a time where ranked is down. Pre-season 5 starts after season 4 ends and an ELO reset will occur where you no longer have any points and you play 10 games where, depending on your win rate, it re-places you. USUALLY you drop 1 league, (e.g. Plat goes to gold, gold to silver, silver to bronze, bronzies are bronze for life).
Is there a defined start and stop of the seasons?
Yes, they will announce the end of season 4 and start handing out rewards based on what elo you were before the end. Then pre-season 5 starts until season 5 is actually starting. Seasons are essentially just for the pro´s. For the average player, it´s the yearly ELO reset and awards.
What are they
Soon after world´s in the end, and a few months later is when season 5 starts.
Any type of season info or what to expect in the next few months would be great! Thanks!
Massive balance changes and awards are handled during the pre-season period. (e.g. your icon for season 4, maybe a skin for being gold+, and a major change such as pre-season 4 where they re-vamped the itemization for bruisers).