Howdy! I hope my answers can help you out.
First off, I'd recommend having a look at the demo video for Plunderlust, our spin-off game for Vast Grimm. It's the second video on the kickstarter page here: https://www.kickstarter.com/projects/creaturecuration/plunderlust-trading-card-g...
On to the specific questions:
What happens if I haven't drawn a location card, or if I haven't drawn an enemy, or if I don’t have enough silver for an enemy (lurk phase)?
-- When playing solo, if you haven't drawn any Monsters, then you are safe from Monsters until you draw some! No worries there.
-- If you haven't drawn a Location, then you can't play a Location. If for whatever reason this means that you have no Locations in play, then you will have to play the highest cost Monster in your hand to fight. If there are Monsters in play and you cannot play a Location from your hand, you will have to keep fighting those Monsters. If there are no Monsters in play and you cannot play a Location from your hand, you can still choose to Explore a Location that is already in play.
-- Keep in mind that you aren't actually spending your accumulated Silver to play Monsters on yourself during the Lurk Phase. You are simply playing Monsters that cost less than or equal to the amount of Silver you rolled during Exploration.
Can I simply choose a card from the deck during the buy phase?
-- During the Buy Phase you can purchase Scum and Equipment from your hand, not from your deck.
In the explore phase, if I play a location card, do all the monsters in my hand attack me?
-- After the Explore Phase, during the Lurk Phase, you will play Monsters that cost less than or equal to the amount of Silver you rolled during Exploration. Then, during the Fight Phase you just fight the Monsters that are in play.
How much equipment can I carry with me? Do I keep my equipment from round to round? How many sums can i have?
-- You can carry as much Equipment as you like, no encumbrance, and it sticks around from round to round. Only "one use" Equipment gets discarded. Likewise, you can accumulate as much Silver as you can loot.
Happy Gaming!