Adding infantry, static units and even vehicles to Support Formations is good if the enemy gets a breakthrough. That allows non-artillery units to attack them and thus the infantry and such could, would and will fire back. During bombardment... they're meat shields. A few PWL w/ the Non-Combat box ticked can be helpful if you can get them fortified. Maybe an MG Nest (CAP-Static) or tow as well, with some infantry. Throw a couple of APCs (CAP-Light Vehicle) for the armor bonus and they should be fairly well protected. Don't spend too much on them though.
As for Long Range Bombardment. It's basically a bigger Medium Bombardment, yes. However, Medium Bombardment can only hit Support or Front Line formations, while Long range can hit those and Rear Formations too. So it's less of a bigger Medium Bombardment and more of a Medium Bombardment with Heavy Bombardment range for less weight than a Heavy Bombardment.
Putting Bombardment in the Front Line is as such:
Light Bombardment, as I understand it will not benefit at all, at least not as bombardment weapons. They'll just attack as any other unit. Any AA weapon does this as well, but also functions as an AA in addition to it.
Medium Bombardment can conduct counter battery fire during the bombardment phase and attack during the main combat phase which precedes it. That is my understanding at least.
The same holds true for LR and Heavy versions, just with better range.
YMMV, and I have not thoroughly tested it yet to confirm.