Having lived in a C2 with C4/HS for the last 6 months I'm comfortable saying C4s are good money for people who don't have the manpower for/don't feel like running Capital Escalations in C5s.

You can expect about 100 million ISK per site. We run in 3-5 man gangs and this works out to about 5-10 sites completed per hour.

You will not be able to "solo" them efficiently in the traditional sense; if you run 3 accounts you can easily "solo box" them in 3 tengus, or 2 battleships with a Logistics.

They're quiet enough most of the time that you don't have to worry about incoming too much, but I have noticed in the last few months more corps moving into C5->C4s or C4->C4s to run down a chain looking for kills. Using any number of well-known survival tactics you can safely run sites in a C4 with as few as 3 people (sub-capitals) efficiently. If you run in the EU timezone, you don't want to do C4s; there are 3 or 4 huge Russian alliances that are buying up the C4/C3s and the C2/C4s and they're very active in that TZ in C4s. This has put a lot more traffic through C4s in the last 2 months or so during that time window.

Svo.

Depending on the fit he's referring to, it's either remote rep shield fit, which is a little slow DPS wise, or local uber tank, which can be a bit expensive. Still good money though. Integrated Terminus' are the easiest btw; you'd roll them no problem, we used to do dual RR tengus for those.

Svo.

As several people hinted at about C4s are the sweet spot for 1-2 people with well rounded sub-cap skills (but don't have or aren't interested in moving into multiboxing capitals or joining a bigger corp). A small number of well organised/skilled characters can run thorugh C4s quite effectively without having to spread the payout over lots of people.

Routes to k-space are going to be an issue, a C3 static could potentially mean you can crash it constantly for 2 hours and find nothing but C3s with low/null links and incoming C4s before you find a d845, k162 from high or a low thats feasible for highsec logistics. But a C3 static gives you another chance to make ISK if your motivated as you won't have to crash many to find one with lots of sites built up.

There is apparently a wandering hole from C4/k-space, most people are of the opinion that it doesn't exist in the game, I'm not so sure myself as the chance of it appearing does mean you could sit in a C4 24x7 monitoring sigs for 2-3 years and never see one, but that does mean its pretty much irrelevant if it exists or not and no ones ever come forward and said they've seen one.

To a degree yes - tho a 30man active corp in a C4 is wasting their time when they could be pulling in far more in a C5/6. C2/3 is better for a casual corp with mixed skills tho than a C4/3 as when activity is light then they don't have the potential to run local sites so easily - theres going to be some crossover tho. i.e. if they are very active in running their static then a C4/3 could make more sense.