- What was a proposed alternative to Segwit?
Bitcoin cash (increase of blocksize).
- What did Segwit solve more than just the scaling issue?
It fixed transaction malleability. (signatures and scripts can be changed without changing the transaction id).
- How is Segwit and the Lightning network connected?
With Segwit there is the possibility for second layer solutions like the Lightning network. It will boost bitcoin’s transaction capacity by taking frequent, small transactions off-chain and settling them at a later time.
- Are people, wallets and other services forced to use Segwit?
No nobody is forced. Not every wallet support Segwit (yet). But most (hardware) wallets do nowadays.