Do I need a Bitcoin full node in order to use BTC RPC Explorer? I'm thinking of using https://github.com/janoside/btc-rpc-explorer as my json explorer, but I run a pruned bitcoin node. Will this cause issues when running btc-rpc-explorer if I wanted to query old data? And if so what is the appropriate pruned node amount to access 1-2 years of blockchain history?
Will this cause issues when running btc-rpc-explorer if I wanted to query old data?

Yes, as it requires txindex.

And if so what is the appropriate pruned node amount to access 1-2 years of blockchain history?

txindex is currently only supported without pruning, so you need to have a non-pruned bitcoind to use btc-rpc-explorer.