I can't make any recommendation about battery monitors. Seems like I've seen a few models mentioned in these forums, but I'd be hard-pressed to find them... external search along the lines of "site:skoolie.net battery monitor" on your favorite yahoo/google/bing/duckduckgo/etc could be a good place to start.
Higher amperage will charge a battery faster, which most people consider "better." Depending on the size of the battery, it could also ruin a battery faster. There are various guidelines or rules of thumb as to the recommended charging rate. Mostly it depends on the amp-hour capacity rating of the battery bank and the battery construction (flooded lead, AGM lead, etc). There wasn't any mention of your battery bank's size, nor whether you prefer a permanent-install charger or something portable, so I've just mentioned the two I have experience with. I've used that B&D at 40 amps charging a series pair of J305P-AC batteries. These are rated 330AH at 20 hours. Trojan's "Battery Maintenance" web page
says "When selecting a charger, the charge rate should be between 10% and 13% of the battery’s 20-hour AH capacity." I was at the high end of that range. Charging below that guideline is perfectly safe, but it'll extend the charging time. The recommendation may be different for different manufacturers or battery chemistries.
Confession: I sometimes use that big charger on that trailer I mentioned earlier when I'm in a hurry. It has an automotive-size deep cycle battery, maybe 80 AH I guess, and I sometimes start it at 20 A or occasionally 40 A charge. It tapers down pretty fast from there. In this case I accept the trade-off that fast charge might shorten battery life as being better than the damage a customer will do if he runs this battery until it's very deeply discharged (because I sent it out less than fully charged), or the inconvenience to me if I have to go out and charge or replace the battery while it's out on a job.