The intro promo for Internet only is going to be a flat discount (usually $19 off). You can change your speed anytime and the discount stays the same and only the base price changes. If you do the self install you will be responsible for the wiring from the NID to the modem. Like AMDUSER posted, some customers will DIY a full tech install (run a clean pair from the demarc to the modem), and contact support to order the higher packages if the line will support it.
I live in a large apartment building, so no possibility of running my own lines. I guess I won't count on Max Plus working, but Max is already potentially faster than my current TWC service.