gloves ,goggles are a must
I'd go with fox dirtpaw/pawtectors -there only $30 and have lasted me for years great glove
Goggles -just make sure you get some decent lexan antifog lens , tear off posts and silicon on the strap i'd go with some oakley crow bars
Helmet- buy the best you can afford , shop around for specials , go to the shop try some on find the right one and then go looking for it online to save $$$
Gear wise: I like thor gear , I personally think its the best stuff out there and heaps more comfortable than the others. If your riding a 50 i reckon 3/4 jersey's are the way to go and there a looser fit and you can still run conventional pants rather than baggies. try and get the same colour and brand and get some gear that is original and stands out rather than the norm colours if your gonna be a show pony
boots: no need for em on 50s unless you have rooted ankles , 3/4 boots are good such as slammers , icons or tech2's but stay away from full length mx boots you cant ride 50s in em
hope that helps