Hi
on 1: I am quite sure with decent cooling and good power limit values, this should not limit you much, though it is questionable for me if it makes sense to grab low tdp model for oc, which will also become clear at 2
on 2: You can not override the multiplicator, the max is not negotiable for Intel on non K chips - you will need a much higher bclk for 4500 for example than on normal 6400 if you use a T-model
on 3: I have no experience with T-models, but in gerneral high bclk at full multiplicator is hard to stabilize, on i3 and Penriums I hit voltage limits before I hit BCLK limits though, 33x150 at Pentium G4400 is nearly 5g and you cannot set ratio in BIOS to 30 for example, so I hit air limits around 4,8 for example with 1,4v+. In my opinion, a high bclk above 200 can be quite hard to stabilize for daily use, you might need to raise some subvoltages which then produces more heat.
The idea is nice, taking low tdp model, but as resummee I am not sure this is best solution when you want to get at decent daily oc of 4,4 or above