Even in the "good ol' days" when vehicles ran on Red Arrow time instead of SEPTA sort-of-time, 4 minutes would be cutting it too close. Remember that you have to make it from the trolley bays through the terminal to the 100 platform. That's at least 2 minutes, and will be more if you have to swim upstream against a crowd emptying from the El.
Also, if you're not familiar with the system, my standard rant,rant,rant about fare payment:
NEVER, EVER PAY THE $2 CASH FARE.
For a short-term trial you'll want to stock up on tokens ($1.30 each compared to the 2-buck "sucker" fare) and plenty of quarters and dimes for the transfer that you'll buy when you board the first vehicle. You'll also need dollars if you're taking the 100 beyond Bryn Mawr where the second zone kicks in. Unfortunately I don't remember if the 102 also has a second zone.
For longer-term use you should get out your calculator and see if a pass would work. The Transpass might be your best place to start because it is good for one boarding anywhere. That means you could use it once on the 102 and again on the 100 w/o paying a transfer charge. The only extra would be any zone charges. You do have to do the math each month, though, 'cause depending on your travel plans there's no guarantee that you'll break even with a pass instead of tokens.
In general for a trip such as yours the Cross County pass is more expensive and a TrailPass is
much more. The TrailPass's cost is based on the higher-priced Regional Rail fare structure, although the helpful
people at SEPTA will be glad to recommend that you buy one for riding the trolley .... uh, I think I'll "pass".