Sentencing overview in very general terms follows. Custom/practice/procedures/results can vary a bit from district to district and judge to judge.
LAV is facing an absolute statutory maximum of 25 years. 5 yrs on the conspiracy re the mgs and 20 years on the sanction stuff. That sentence would presume the the max was imposed on both and ran consecutively. While legally possible, such a result would be EXTRAORDINARILY unlikely as to both a max out and consecutive sentence under any circumstances, particularly if he is in fact cooperating.
The sentencing in the first instance in federal court is determined by 3 things:
A. The statutory minimum and maximums of the law violated and pled to
B. The application of the the now advisory US Sentencing Guidelines
C. the application of the statutory sentencing factors found at 18 USC 3553 i.e. history and characteristics of the defendant, the need to promote respect for the law, deterrence etc. all with an eye toward imposing a sentencing which is sufficient to hit all those points but no greater than necessary.
As posted before, the anticipated guidelines are an offense level of 25. Presuming a criminal history category of I, that yields a suggested guideline range of 57-71 months
https://www.ussc.gov/guidelines/2021...2021-chapter-5
Sometimes, that offense level can go up due to certain enhancements i.e. role in the offense, amount of loss, abuse of a position of power/trust, special skills used to commit the offense etc. It is difficult to predict which enhancements will be applied without really knowing the file and/or reviewing the pre sentence report which has not even been drafted yet as he just pled guilty.
If he is in fact cooperating to the point that the USA filed a motion for downward departure based on substantial assistance, the judge could sentence him to probation. In fact, as there is no statutory minimum, a judge could do that anyway though that happens very rarely when the guidelines are at this purported level and there is no motion by the govt.
Re risk as a cooperator in the BOP.
As others have stated this tends to be more of a thing with other folks. Having said that, one can stub their toe in the BOP with other inmates based on omissions/commission that occur on any given day separate and apart from any cooperation, real or perceived.
As to the Min Security placement- IIRC, any sentence over 60 months precludes that initially. I concur that it makes sense to send him the FMC Butner in the first instance given his presumed medical needs and home. Having said that, if his cancer is really driving the train and the best BOP oncologist is somewhere else, he could be somewhere else. BOP actually gets it right most of the time with sick folks. BUT, I have had more than one "healthy" prisoner finish out their camp time at Yankton in SD where it is cold, cold cold v the camp at Leavenworth right up the road from home. Notably the Federal Medical Centers can and do handle all prisoner classifications from min to max.
If the guidelines are in the 5-7 year range and he in fact provides substantial assistance, an incarceration sentence could still be in the cards. While the defense would argue what he has done in the past and he is sick, a prosecutor could turn the MIL/GOVT experience against him and argue that when you deal in machine guns and with foreign powers, folks got to go to prison as a deterrent to others.
Even if you reduced the low end (50 months) by half, you are still talking a couple of years "behind the wall" so to speak.
Good Time Credit
Unlike many states, GTC is limited to 15% of the sentence and runs at the rate of 56 days per year max on any sentence that is 12 month and 1 day or more.
WILD SPECULATION
Based on my training and experience, in my district, in front of virtually any judge, his defense atty would be telling him to buckle up for 24 months minimum presume a total offense level of 25, despite the filing of a substantial assistance motion by the USA.