Well, first of all I don't think you can sight in a ventilated rib barrel. Now to your questions.
1. You're on the right track with the modified choke. Although, many will tell you to use a full or even an improved cylinder choke. I would start with a modified, and decide for yourself if you want a bigger or smaller spread. You can also invest in an aftermarket choke. Many people, including myself, prefer Patternmaster chokes. And as far as patterning goes, just buy different loads and see what works best.
2. For gobblers, full, extra-full, and super-full chokes are probably the most popular. All of those are made by Remington. Again, aftermarket chokes can also be bought for turkey hunting. Do the same thing for patterning as mentioned in #1.
3. Type of choke? Most people like the full choke and some times the modified if they come in close. Goose hunting is where Patternmaster chokes shine. #BB and #BBB are the most popular shot sizes for use on goose.
Things to know....(that I can think of)
- BE SAFE!!!!!!!!!!!!
- When shooting slugs through a ventilated rib barrel, always use an improved cylinder or true cylinder choke. Or a rifled choke which is specifically designed for use with slugs.
- Clean your gun frequently and oil it lightly with Rem Oil after every time you use it. Shotguns CAN rust very quickly, especially when exposed to the wrong conditions (high humidity, rain). If you oil it lightly when your supposed to, you can very effectively prevent rust.
- Try to buy steel shot loads with velocity in the 1450 - 1550 F.P.S. range.
Good luck hunting in the coming years.