Need some advices for USF

I'm fairly experienced with the game (500 hours), but at least half of it I spent on campaign and Theatre of War. I decided to main USF and play it. After a while I learned more and more, untill I started dropping from my ranks (was at 6, now at 3). Frustrated at losing as UKF, I started playing OKW. To my surprise, I played OKW without any problems, and I have reached rank 8. I don't know why its happening, but maybe I'm just playing wrong, so I will list off my average match

I start by making 3 rifleman squads, (not echelon, I know they're worse) after a while I get enough fuel for a captain. Meanwhile, my 3 rifleman squads fight struggle with MG42s and Sturmpioneers (mostly them, but sometimes my rifleman struggle with other things). Sturmpioneers aren't as bad, but sometimes enemy overwhelmes me with them. But the worst part is MG42s. I try to flank them, but the enemy also attacks me with Granadiers or Volks, meaning I have no manpower for defending and flanking. After this engegement, I reatreat, leaving my enemy to make defences. For some reason, I dont have enough ammunitions for anything ( even though I didnt spend much, leaving me with no Browning (doesn't make sense to make mines), but I have enough fuel, so I buy AA gun to help my already weakened infantry. Then I lose it to some armour dive, beacause they have more fuel than me. I lose and lose more man, so I get a Major, then, a Sherman. It really helps with those elite units. But then enemy brings in P4 or Panther, and we know P4 or Panther > Sherman. I get more shermans, but then more tanks come in, including king Tigers. Frustrated, that the tiger always attacks, kills a bunch of stuff, and then leave makes me frustrated, making me dive the tiger(my bad) .Then I gradually lose everything to infantry and tanks( sometimes artillery) and then lose. Also my commanders are the Airbourne one, ranger- calliope, and Pershing doctrine. I hope it was specific

I assume you talk about 1v1?
My usual build order is 3 Rifles into first officer (I prefer Captain but I mostly play 2v2 and 3v3), followed by ambulance, LV (AA half track/Stuart), Pak howitzer/ATG depending and weapon racks on the battle. Afterwards major into either Jackson or Sherman.
Double officer builds are viable too, although more heavy on manpower. But they give you good options for the late game.
In general I prefer to spend munitions on BARs, but if you go Lieutenant you should probably rather use them on Bazookas first to keep up against LVs and supplement against a P4.
In general I think USF has the biggest whole in the line up while waiting for the first officer to build. That's just a phase where you WILL be pushed back. If the enemy tries to lock you down with MGs, I would surely build an LV.

Especially while you only have 3 Rifles, I would sacrifice some map control and keep them tighter together in case you run into Sturmpioneers. After that it's mostly a run on munitions to get your units BARed up to compete with STGs. Once you reach that point, I would refocus on fuel for the first tank.

For the late game I would not recommend Sherman spam (1v1 is different, but you need to get your timings for pushing correctly otherwise it's just a bunch of dead Shermans). At least team games fair better with going 1 Sherman + 2 Jacksons. If you go for four vehicles, I would recommend a Calliope (which I would build after the first Jackson). Otherwise the Scott or another Sherman will do fine as well.

I exclusively play USF. Big advice, first thing to learn as USF is how to use riflemen to beat all of the different axis infantry. There's not a 1-2 step guide, you just need to get familiar with how much damage RM do at different ranges and how much beating they can take. Success rides on this and RM are capable of this even Panzer grens and Obers.

For close range units like assault grens and Sturmpios fight them at long range until you drop a model or 2 then just shoot at them even if they approach. If you can't fight them at long range cus they are are too close then out number them. One strat is to path away and bait them into another RM squad that is just standing and shooting. Also I recommend using the RE as a combat unit, they are good to add a bit more health and damage to your force and if the enemy is stupid enough to focus them it will enable your RM.

Against volks and grens you can close pretty rapidly and still win. When volks get STGs you still want to be somewhat close because they seem to still beat RM at long range but you can't fight them point blank anymore. Against Obers/grens you need to close fast because LMGs do less damage at close range. One trick that works against inattentive players (still works at rank 14 lol) is to bait the enemy into shooting at a RM in green cover and then close the distance with a second one. Sometimes they won't switch to the advancing squad so you can get close without losing models.

For fighting MG42s: early game don't try to brute force through them, if you take fire path away. I try to stay out side the MG42 radius while using all my riflemen to focus down any grens/pios they let me shoot at from safety. If you can get around the cone of fire for a flank do it. One RM can solo a gren or pio and kill the machine gun. Focus the MG with the flanking squad as much as possible but you might need to first kill protecting squads if they are close enough to really hurt your flanking squad. If they pick up the gun to reposition it then have all squads path at and attack the MG42. Keep your squads spread, you want them close enough to be able to focus the same enemy but far enough not to all get suppressed at once. If the enemy is good at positioning the MG42 just avoid it until after you get an officer. After going RM -> RM -> RM -> LT/CPT get grenades. RE/Officers can fire smoke grenades. These are key to fighting MG42s, fire them as close as possible to the MG42 and then throw a grenade on them. Also make sure to keep the RE/officer ahead of the RM so only he gets suppressed by the first burst, with smoke grenades its trivial to beat MG42. If the enemy keeps building them (like 3-4) then you can buy a mortar to help. Also don't fight MGs if you don't have ~50mu, you need to have enough for at least one smoke+grenade combo.

The next thing I recommend is making a point of getting both weapon racks and grenades. It is a very good idea to upgrade bazookas on RE after getting officer (unless you are sure your enemy is not getting light vehicles), this reduces the Chance you get cheesed and also will help you in medium vs. medium tank fight.

Also if you are fighting OKW and they start using MG34s I also recommend teaching grenades asap.

Update: I tried what you guys said, it wasn't perfect, but it is certinally improved. Over time I believe I'll improve using this build order/strategy. Thank you so much!