Questions and Answers

I am 15, am a huge avation geek, and I love flying (even though I don’t get to often). A family emergency has come up and I am going to be flying out to Baltimore (on my own) in about a weeks time to help my grand ma. Based on the tickets I have looked at (haven’t booked yet, my dad wants to wait for some stupid reason) I am going to have a stop in LHR. I will arrive in terminal 2 (on Are Ligus) and depart terminal 5 (BA). The layover will be about 4 hours going out and 2 and a half coming back, so time isn’t that much of an issue, though if anyone knows of anything fun to do incase my flight gets delayed or my dad books a different flight, I’d like to have a backup plan. Other than that, I just have a few questions to make sure it goes smoothly.
Note: Although I don’t fly often, I have flown on my own before and had no issue, though it was a direct, US domestic flight on Southwest, so my cat could probably figure it out.

So: Does anyone who fly Heathrow often have any transit tips on getting around. I believe I should just follow the signs to the busses that go between terminals. If anyone knows how long this takes (between the bus and clearing any additional security between terminals) that would be a huge help.
Next, as I said, I am super into aviation, so I love to be near the runways and taxiways and what not, so if anyone has any tips or areas for “spotting” ( I low key hate that word) that would be great. And yes, I know Heathrow has a spotting deck, though it is in terminal 4, which is south of all the other terminals and seems to be too much out of the way, so again for the people who know Heathrow like the back of their hand may be able to tell me if there is anyway possible I could get over there (I really hope I can).
That’s all I can think of, so I guess I’ll update this if anything else comes to mind.
Thanks, Rhys