[steveh11]

One tactic I'm considering is the "troop swarm". If I sent in dozens of troops-laden scouts with PD and ECM, some of them ought to make it down to the surface, surely.

Dunno how it works in simultaneous, but in 'normal' play each troop landing causes 10 rounds of ground combat. You're not going to get enough troops on a bunch of Scouts to avoid (extremely expensive) defeat in detail.

What you have to do is accept that you have to go into deficit spending, and 'get it done' before you go bankrupt. That's not going to be easy with a small homeworld, mind. You might have to spend some time building up your storage first. How long are you prepared to wait?

Of course, the other thing to remember is that if you take out all his other worlds, just blockading his homeworld will stop him building or maintaining other units - at least, it did when it happened to me! - so maintaining a blockade while you build up is important.
Steve.