Luchs:
My opinion is you can't do shit vs a well microed Luchs. There are too many shrecks on the field the moment your Stuart hit the field to be a treat to him or he seriously fucked his micro. I prefer to go Lieutenant + Zooks + Half-track to take the volks blob suppressed and try some hit on the Luchs but guess what last time I tried to kill a Luchs with zook, it missed 2x2 volleys in a raw, can't help vs bad luck.
So eventually you'll take the Luchs out to face the Pz4 or Panther afterward.
Why I also prefer the Half-track: Both the HT and the Stuart are pointless vs the OKW Pz4 and Panther. I mean ok, a Stuart is interesting with the stun + an tank in support, but here again, what do you do vs the shreck blob? Better having a HT to suppress the blob and Zooks + tanks vs the Pz4. With a bit of micro I manage to save the HT quite a long time every game.
In addition it become a source of frustration for the other player so he may lose his temper to kill it and do something stupid that can benefice you.
Early game:
It is sad to say but, blob.
I send my RE capping and keep my rifles close to my cutoff until I have 3 squads. I fact, I let him attack the first round. Your RE should be able to take down the Kubel alone with some micro.
And then I start blobbing with 3 rifles asap, my goal is to seek confrontation and focus fire on the sturm, ideally I take it down. And repeat.
Lieutenant
Once the lieutenant bought, it depends on the map and how you are engaged, M20 to harass his fuel or .50 to use it with your blob. Yes use the .50 with your 3RM. It is easy, you send your blob A-move in a direction and when you start fighting you keep microing your RMs squads, the .50 setup alone and start suppressing from behind.
Zooks: equip your zooks on RE
HT: keep the zooks close to the HT and use it as a central point, always keep your RM in front of them and if you have to hard retreat all of them, retreat the HT as well.
Panic button
If I can't kill the Luchs fast enough, it also means I didn't cut if fuel or took enough advantage so I expect Pz4, In this case I go Armor for a fast M10.
If I took the Luch and I'm confident I can handle him, I go Major first or not, honestly I'll probably go Armor in any case
Personally I end up many games vs OKW with 2x.50, I use 1 for capping and harassing and 1 to protect my flank. Just A-move it so it only set up when he sees enemies.