When sending a transaction between wallets I own is it best practise to add lots of decimals? For example instead of sending 0.0042 btc, I should send 0.004268942?
The privacy risk with round number payments is that usually (but not always) the round number is a payment to someone else. This means that the other non-round output in the transaction is usually the change. This allows someone looking at the blockchain to see which output is a payment, which output is change, and link the change address to the input address.
Now, if you are sending money between your own wallets, then there are other things to consider too. If you spend an input (or all the inputs from one address) in full and send them to another address, then that is also usually an indicator that the two addresses belong to the same person (or the output address is a deposit address at an exchange or other service belonging to that person's account).
Also a bit scary (I don't use a VPN and checking an explorer from IP can footprint to my bitcoin addresses)
Just use Tor to look up your addresses on a block explorer then. It's free and better for anonymity than a VPN anyway.