a dry bag with D-rings on will be good for stuffing a sleeping bag into and strapping to the top of your rack. Tent packs will do the same.
Travel light though. One pannier bag should be enough for your clothes and cooking kit. The other could take your sleeping bag and thermarest. Only then need to stick the tent on top.
Bar bags are good for day to day items – phone, map, pens, torch, compass, splashtop. Get one with a shoulder strap so you can sling it over your shoulder like a man bag when you leave the bike.
ANy effect on handling of any bags you get used to in the space of a few miles and dont notice by the end of the first day.
2x thermarests in one roll bag and the tent in the other.
Bedding for both in one saddle bag with clothes, cooking equipment in the other with clothes.
More photos to show bags.