401k 钱是你的 (if it is vested),投资受益受很多因素影响.这要看楼主如何看啦. In fact US house price increase in general is bearly better the inflaction rate in the past a few decades (except both costal areas). Rent depends on supply/demand and housing price too in general.
Every employer could have slight different rule governing the amount you could borrower against your 401K. Normally, it is less of $50K or 50% of your 401K balance. In another words, the maximum is $50K if your balance is >= $100K. If balance is smaller, then 50% of your balance.
If you get loan from your 401K and you pay back according to schedule, there is no penalty at all. There is no income tax at all since this is not withdraw.