So my question is, apart from electrum wallet which other wallet is the safest for long term holding of bitcoin?.
Beside Electrum wallet, you can use Bitcoin Core, full node if you want best privacy with Tor connection, or prune node if you are not serious about privacy.
Hardware wallets if you can buy them.
[LIST] Open Source Hardware WalletsWith the current reduction of price in Bitcoin, is it the best time to buy bitcoin or should I still wait for the dip?.
Best time to buy Bitcoin is when you stop thinking, hesitation and start to buy it with your spare money without pressure to borrow money for investment.
Because you can not timing the market, can not find bottom, stop worrying about best time.