I used to hold 2-3 months cash on checking account, but rest in taxable investment account.
Reg high credit cards, we should avoid it as the rates are around 20%+. HELOCs are perfect backup plan. However, banks may freeze during recession period (it depends on bank and at that situation). JP Morgan froze my HELOC during 2008-2009, but that was real estate recession.
Invest the cash wisely to grow higher, use it to buy real estate when you see correction on real estate prices. HELOCs can be used for next purchase, but banks may view HELOCs differently.
If you have 100k HELOC and use it, when you go to mortgage, they deduct 1% ($1000/month) as your monthly liability that will be deducted in your DTI eligibility.