Why do you say that? I think I may actually play out cheaper than other empires. Lower tech costs less, and I won't need some pieces of tech as much as others. Lasers don't really need the range modifier, for instance, since they'll mainly be used for point blank piercing, so I can shave off costs there. Engines may not use fuel-per-hour modifiers and scrimp on costs. If I'm lacking resources that means I'll need to claim more planets! It will be extremely aggressive as well, possibly unable to stop exploiting. Attack one NPR, and while recouping the cost by colonizing their worlds, encounter another NPR. That means getting into another fight, and recouping costs... Either way, Earth will probably be permanently producing mines, and terrifyingly sized mining ships will likely become a thing.
If you are going the route of tech assimilation via boarding, microwave weapons may actually be a good investment to knock out the enemies ability to shoot at your boarding shuttles. Also don't forget to have maintenance supply barges accompanying your fleet train, so your prize vessels can repair themselves enough to make it back to your chop-shop planet. Salvage vessels would likely also be a good idea following this strategy so you recover some tech from ships you accidentally destroy instead of capture.
40 million kms at 30000 kms? Dayum. I knew missiles were good and could be extremely long ranged, but I don't like creating overpowered, across-the-system missile frigates. Then again, with my current knowledge of the game, no matter how hard I try i'll never make anything too good.
40 million km really isn't long range.
What's the best weapon to use for point defense?
Usually a mix of anti-missile missiles(AMM's) and beam PD works best, backed up by shields so that any leakers don't cause any lasting damage.
AMM's are short range(<2 M km), typically warhead 1, missiles with the best combination of speed and hit chance that you can manage. They are typically size 1 so as to carry the maximum numbers on each ship and take advantage of smaller launchers firing faster. However, particularly at low tech or if facing armoured missiles and so needing a larger warhead, it is quite possible to use size 2 or 3 missiles in this role. If you rely purely on AMM's for your PD, you will usually need to fire multiple AMM's for each incoming missile.
As for which type of beam defence is best, it varies depending on what the enemy is firing at you. Mesons are good against armoured missiles, but can more easily be overwhelmed by numbers. Lasers are also good against armoured missiles and have the range to potentially get multiple shots at an incoming salvo, but again are subject to being overwhelmed by numbers. Gauss(once at least a couple of levels of the rate of fire tech are researched) fair poorly against armoured missiles but are excellent against large numbers. Railguns do well against armoured missiles and also against numbers but, as they cannot be turreted, have difficulty hitting fast missiles.
CIWS are self contained gauss PD that include their own firecontrol and that can be mounted on commercial designs as well as military. Unlike Gauss PD however they can only fire on missiles that are attempting to hit the ship it is mounted on rather than any ship in the taskgroup.