For 5 gallons, I would save my money and use oak beads..
For most winemakers, a barrel is used to help add complexity to wine. Most winemakers are really looking for the following three benefits...
1) Flavor - A variety of flavor components from raw wood to vanillas to chocolate. Tannins are also imparted to the wine. The type of flavor and its intensity depend greatly on the toast of the barrel.
2) Micro-oxidation - Wood is not a perfect seal. It actually breaths allowing for minute amounts of oxygen through to the wine. This, in turn softens the wine.
3) Evaperation - Wood is absorbant. This allow the wine to evaporate over time (to a small degree). This has the effect of intensifing the wines flavor.
I get these benifits, well, consider the following..
These benefits require a careful retraint. If too much of it occurs, you will be in danger of ruining your otherwise great wine. These benifits must happen very slowly over time.
So how do they control it? Well, they do this by controlling volume respect to the total surface area inside the barrel.
In other words, If the barrel is small then the amount of surface area will be high and the volume it holds will be low. If the barrel is large, then the volume will be high and the surface area will be low.
So, barrels that are big will have less effect on wine, then barrels that are small.
The optimal size seems to be around 225 liters or 59-60 gallons. This is what most professional wineries use. This size seems to yield just the right amount of oak, just the right amount of micro-oxidation, with just the right amount of evaporation, and in just the right amount of time.
For a brarrel of 5 gallons or so, the surface to volumne ratio is too high. Using a small barrel line this puts your wine at risk of macro oxidation (yuk) and over-oaking. The amount of evaporation/absobtion (what they call the angel's share) can also be excessive.
If you do use this barrel, you need to keep an eye on it!. Top the barrel off (keep it filled) often. Taste often and take it out of the barrel once you detect any problems.