1. Can you make a pact with the lurker and exhaust it to gain power in the same turn? Pacts are made at the beginning of the turn and the pact is used during upkeep so this seems to make sense.

2. Do monsters with ambush immediately begin combat with you if they move into your area or appear through an encounter or do you get one chance to evade and then you are stuck in combat?

1. I'd say yes - the order operations happen in upkeep is up to the investigator so why not? Otherwise they should have said the card entered play exhausted.

2. You still get your initial chance to evade. It's only once combat begins that you can't evade. The only monsters you can't evade initially are ones that surprise you (Dark Pharaoh encounters).

1) Yes

2) You can evade ambushing monsters before combat, but you can't flee from them once combat starts. (They make a very unpleasant combination with the "a monster surprises you" encounters from CotDP)

Thanks, you think entrapment would have been a better name for the ability instead of ambush then.

Grapple would also be a suitable name for that.