I'll take a stab at your questions, Moonlight.
- When restoring an older, especially dried-out glove, I will usually give it anywhere from one to three light coats of lanolin, depending on just how dry the leather is.
If the glove is only being displayed, or stored in a clean, dry, room-temperature environment, the leather treatment might last several years. There's not really any need to reapply the conditioner often unless the leather begins to dry out again. If the glove is just sitting on a shelf in cool, dry conditions the leather should stay properly moisturized.
You might take it down from time-to-time and give a light coat just for the sheer enjoyment of working on your glove!
If it's a "gamer" glove being actively used in hot, dusty field conditions, I'll wipe off any accumulated dust as needed and maybe hit it with a light coat of conditioner a couple of times a year to protect it from the elements and keep it soft and flexible.
- I generally use a clean cotton rag to apply conditioner, but have also used a sponge, towels and even the terry cloth pads used to apply automotive waxes. For the best results, apply the conditioner to the rag and not directly to the glove. This helps to avoid oversaturated spots on the glove and gives an even coat.
- There isn't much you can do when a sewn seam begins to pull apart other than treat it gently to avoid further damage or have the seam resewn. Sewing leather takes some specialized tools and can be fairly costly.
Seam deterioration is usually a problem with older (pre-1950's) gloves because they used cotton thread that weakens over time. Most gloves after that point use nylon thread which is much more durable.
Hope that helps!