A quick check says the whole litecoin network has a nethash of about 17.000 Gh/s. You have about 150 Gh/s. So you would provide slightly below 1% of the whole network. Statistics say otherwise and a more likely to be right, but just as a quick guesstimate you should solve every 100th block, a little less actually. With blocktime of ~2.5 minutes that means one block roughly every 5 hours.
Please remember that this is not precise at all and just a lot of guesswork.

The only difference between pool mining and solo mining would be the rate of payouts recieved. Either once every ~5 hours or every time the pool solves a block.

As I trade coins mostly, I'd be interested to have them as soon as possible, hence pool mining. If you want maximum profit, go for solo mining.

Concerning the selling of hash power, I haven't checked their offers but considering you have a lot of power, it is unlikely that they will be able to put it all to good use and therefore you should earn less than you would with mining yourself.

I am far from an expert on that though, so please feel free to correct me on that.