generally the idea is that LSP commits to the fee structure at the time of the purchase (lets say i'll keep the fees at 100ppm for the duration of 1y). None of it is really enforcable so its more of a promise and reputation of the lsp to keep it.

In reality you want the LSP to be making money from your channel as that incentivizes it to keep it open forever. Of course how much and how is up to the market to figure out - maybe you prefer to pay a larger sum upfront for the opening and have zero outbound fees for the duration of the contract, or maybe you prefer to pay a fee every time you use the channel but have cheaper upfront payment (mostly to onchain fees otherwise the lsp is exposed to an attack vector)