How do you scout/harass/attack/deal with choke points in early->mid game in Starcraft?
All races have 2 scout timings. The first with the worker and an additional one related to your race's tech that usually occurs around the 7 min mark.
Terran: Has scans very early which are not effected by chokes. The most standard scan timing is as soon as your second base has been transformed into an orbital.
Zerg: Most builds come with the assumption you are going to suicide 2 ovies into your opponents base around 7:00 to scout your opponent. Again doesn't care about chokes because they fly.
Toss: The first observer, stargate unit, or an hallucinated phoenix. Again all these hit around 7:00 and don't care about chokes.
But all you need to stay alive and pick your game plan are these two scouts. The first worker can scout any cheesy play such as proxy shenanigans or very early all-ins such as 4-gates. It also allows you yo scout how economically they are playing. If a Terran gets gas expect drops, mines, or hellion. If a toss has lots of chrono expect a 4 gate, if a zerg mines gas past 100 expect banes or roaches.
The 7 min timing lets you scout any tech based all-ins aggression. DTs, Immoral based all-ins, hellbat drops, 12 min roach maxes can all be identified based on this scout timing.
All harass units either fly (banshee, oracle, mutas), are cloaked (banshee, DTs) or are very fast (zerglings and hellions). Flying units and cloaked units are not effected by chokes very much and very quick units are opportunistic, dashing in when the enemy moves out or other units draw them away from the choke.
Harass units are very mobile and as such are also great for scouting. If you plan to open with a build that allows early aggression often the 7:00 min scout timing can be skipped.
As a general rule there is usually no reason to attack a player on 2 bases with the intention of killing them. Notice most of the maps are much more open around the 3rd. If a player id on 2 bases and its not very early in the game they are focusing on tech or army over econ and will be very hard to break.
The exception is you have a large econ advantage and can afford to trade the units inefficiently to finish of your opponent.
If you play a opponent who sits and guards their natural choke the entire game you counter this behavior by taking 4-5 bases and then simply smashing his door down with an overwhelming number of units.