Yes, all of those things will be using up your 4G allowance. The $50 plan is actually 500 MB, not 5000 MB (half a gig as opposed to 5 gigs). Keep in mind that with T-Mobile, the 'Unlimited' plans just drop down to Edge speeds (3G) when you go over the limit, so you don't lose connection you just end up with e REALLY slow connection. That's how they get away with calling 500MB unlimited...
If you have a compatible phone for these plans and don't need a lot of minutes you can look at: http://prepaid-phones.t-mobile.com/prepaid-plans
The last option is $30 USD and gives you the same unlimited data (5GB) and unlimited texting as the $70 per month plan, but only 100 minutes of talk. If you already use something like GrooveIP and forward a Google voice number to it, it only counts against your data and not against your minutes, so you end up with essentially unlimited everything for $30 per month (keeping in mind that GrooveIP and Google voice introduce some delay in the phone call, and you really need to be somewhere with excellent coverage for consistent use).
Final note about T-Mobile, check the coverage map. Where it works well it works very well, but if you're going somewhere without good coverage you'll get spotty reception at best.