I'd say go express to lvl7 where you get the most of useful units, then take your time to raise defences to match HQ lvl and upgrade all the necessary units. After that rush to lvl 9 (or even 10) to get all the new pretty toys and start raising your defences again.
When you upgrade defences you rise your "Base Rating" - now-hidden score showing the relative strength of your base. As BR goes up you get matched with stronger opponents. Beating them gets harder but they offer better loot than easy noobs.
Just be ready that you will lose defensive battles a lot while rushing HQ and offence and keeping defences low. On the plus side, lost defences give you protection from further attacks which helps saving resources.
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