(pushing txs, browsing utxos, etc).
how about using Electrum wallet?
it is a lightweight (SPV) client, it is up to date (meaning it supports SegWit) and works with TestNet. you can run it on any OS by adding the "--testnet" command at the end. on Windows open the properties window of the shortcut on your desktop, go to the Shortcut tab and add that command at the end of Target:
"C:\Program Files (x86)\Electrum\electrum-3.3.6.exe" --testnet
now you can create wallets, import keys, sign transactions, get your UTXO history, broadcast them,...
you can also always only contact the Electrum servers and use their communication protocol to fetch the necessary data you want (basically what Electrum does under the hood). although that would be harder and more time consuming. here is the protocol documentation:
https://electrumx.readthedocs.io/en/latest/protocol.html