The following excerpts are our stance on your questions.
This is taken from the boiler template found in every Mission.
A Note on Loot and Looting
Gamemasters should be careful what they allow players access to, because they can and will try to steal everything not nailed down (and even then, they often have pry bars and claw hammers to deal with those nails). Shadowrun Missions operate under the assumption that two players who have run the same missions will have roughly the same amount of resources available to them (give or take some negotiation and a little bit of minor loot fenced), so when players are able to steal and fence a lot of gear or are able to get their hands on high-priced vehicles, cyberdecks, or foci, it can unbalance the game and make it unfair to players who didn’t have the opportunity to get those items. Gamemasters should avoid letting the players get into a position to do high value looting whenever possible.
This is from the SRM FAQ, Section 6
Can we trade money or gear between players?
Yes, but only within reason. Giving someone an extra gun, or spotting them an extra 1,000¥ for some gear because they’re short is no big deal. However, you should not be giving away large, expensive items or large sums of nuyen. This is primarily to prevent abuse in games where someone is just sitting in to play a session or two, so they just dump their gear and money on their teammates at the end of the game since they’re not planning to play that character anymore.
To set a hard limit on this, gamemasters should not allow players to give away more than 5,000¥ worth of cash and 5,000¥ in gear (using base book value for the gear) per game session.
As you stated, we place our trust in GMs and players. Keeping the AK-97, Browning, and combat knife would be something I would allow at a table as well. I would just remind the player that they need to change ownership (SR5, pgs. 236-237) for any devices with wireless functionality. If I have the same group play, as GM, I would have notes about it so I can enact the consequences for not doing so later on. However, due to the nature of open play, it's not really practical because attendance will usually vary.
As far as the van, I would say no at my table since that's what's in the FAQ.