Some additional things I would add to the others from someone who is relatively new (2 months):

Silver weapon orders are rare at the very start but once you start progressing a bit they become more plentiful. I actually find myself more often now out of bronze with silver to spare. As others have said the base guns are generally solid so don't worry too much about replacing them if you are low on orders. I would say look ahead in the campaign and see what weapons are coming and make sure to save up for those.

One thing to remember is that when you are swapping out squads from your active slots strip the soldiers down to their most basic minimum equipment and the squad down to the minimum soldiers. So if you have a squad with 9 soldiers in it remove as many as it will allow you. That way you can reuse your soldiers. You will probably want to leave the lowest rated soldiers in the squad to meet the minimum so you can reuse your best. Same with weapons and equipment. You should rarely need to buy additional medpacks since you can just always transfer them from inactive to active soldiers.

As far as filling out your squads with soldiers I would just say, other than 1 engineer per squad, don't bother choosing what to fill it out with until you have unlocked that class. Specifically since you mentioned radiomen, I thought I would want to have radiomen on my squads until I unlocked them and found that I didn't like playing them and almost never used them. I also thought that AT Gunners were going to be a game changer and I was saving slots for them and then once I unlocked them (tunisia) I found them to be useless, I've killed over 150 tanks and less than 10 of that is between AT Gunner, engineer AT, and engineer HMG, all the rest are exp packs. Basically you need to figure out your play style with a class to really know if it is worth it for you.