Phil, the first place to start is knowing what your heat loss actually is. If a person doesn't have a good handle on that, all decisions that follow are just a shot in the dark. From that you can determine if you have excess heat producing capacity from your baseboard and get a solid handle on what water temperature you actually need to heat your place. Concerning storage.....if you go with a good gasser that is sized appropriately you can get by with less storage capacity. A common error is to oversize thinking that a larger firebox will "hold a fire" longer. In reality all it does is hold more wood which then smolders during shutdown periods. Something to be avoided as much as possible if you want minimal maintenance, clean burning and long life from your boiler. Many of the gassers in european systems are only working with a couple hundred gallons which could easily be done with something as inexpensive as a pair of old water heater tanks. Not ideal but we all have to work within the constraints of circumstances present on a given job. The flip side of no storage is more time involved rekindling/starting fires, more maintenance and more frequent cleaning. Idling in any wood burner will develop more creosote regardless of what brand it is. So....my humble advice would be to do a heat loss, select the best equipment you can afford and then try very hard to engineer at least a little storage into your system. Those are the three major things you want to prioritize for a functional system with a high WAF.