Weapons being slow are not harder to chamber with, that is not true at all. Actually, there seems to be a slightly larger window with which you chamber if your weapon IS slower. Also, you chamber by prepping your attack as their weapon is almost about to collide with you, not as soon as they release. If your ping is higher, you need to react a bit faster but you can chamber anything with under 100 ping, past 100 ping side wings can hit you before your weapon begins to release unless you can predict the future.
If you want to do chambering practice, I'll help you with it to get your timing down perfectly. I can meet up with you in the duel server some time. Also, most BRD members will help you if you just talk to them and ask for practice of any kind.
Chamber timing varies slightly with weapon types and speeds, so you want to use the same weapon a lot. Chambering is as easy as a manual block IF and only IF: 1. Your ping is constant and not spiking, and under 90. You have blocked 2 attacks from the enemy to know HIS weapon's speed. 3. They aren't holding attacks.
A couple tips; If the opponent is feinting consistently through out the fight, DO NOT TRY TO CHAMBER OVERHEADS, as he will hit you with a side attack before your chamber hits him. However, chambering feints in other directions will hit the enemy before his feint hits you.
If you ever see wallace on the duel server, duel him. He chambers rather than manual block most of the time, and he uses slow hard hitting weapons on a 3 agi build but destroys most people because he chambers as his normal method of attacking. With a little footwork and a certain trick I can teach you to chamber back player's chambers which catches people off guard. Not only that, but you can get it as a good habit and do it without thinking if you practice it a lot. I myself need to make it a habit.
About manual blocking, I myself have this problem but it is mouse discipline and I am trying to fix my bad habits. Firstly, make sure you hold your mouse STRAIGHT. Most people hold their mouse slightly sideways to the left. Fix that. Also, try to move your mouse as little as possible with your block reflexes. I have a HUGE problem with my upper block where I twitch way too far, so after two up blocks I am looking at the sky and die to a side feint. It is my number one cause of death and I am not alone. Your body naturally tends to over shoot movements away from your body with your hand, like in Strategy games such as Starcraft 2 you always want to box units towards yourself as it is more precise. If you don't understand that last part, all it means is move your mouse tiny precise amounts. Takes time and lots of conscious attention to make it a good habit.
Group fighting people have largely covered already. With a strength build you want to get right up in their shit and kill the people who think they can attack you because you have your back turned, etc. With a high athletics character you want to back peddle and force it into a series of 1 v 1 fights with the possibility of suddenly darting forward and picking others off as well.
If you get blocking precision and chamber timing down, feinters will suddenly be the easiest kills for you. Hope to see you in game~