Leverage existing 401k/IRA. Utilize SD IRA or SD 401k?

[Tony Lin]

I've read a lot of material on self directed (including checkbook) options but still not sure the best approach. Would appreciate any advice. 

My situation: Currently employed. Have a large 401k from 7yrs at current company. Have a rollover-IRA from prior 10+ years of employment parked at Vanguard. Maxed annual contribution on both. Would like to use the funds to passively invest in multifamily deals (50-100k), or eventually lead a project myself. I want to leverage as much of the funds in these 2 retirement accounts as possible.

Which of these would best suit my situation? Can both active 401k/roll-over IRA be converted to self directed option? I read that there is investment limit of 50k for SD 401k, are there limits for SD IRA as well? Additionally, would apartment sponsors care if the funds come from a SD format if I simply wire them the funds from a SD account?

Thanks.