If using Test E or C, most will max out the gains from more frequency at EOD. Every day is fine, but it likely isn’t necessary for everyone. I do 50 mg EOD of Test E. More frequency usually is better for E2 levels, and stability of Test levels, but some do seem to like the up and down feeling of less frequency. There isn’t a one size fits all IMO.
IM seems to be preferred. There was a study that said SubQ resulted in better levels, but it was heavily flawed (the SubQ group pinned 2X a week, and the IM once per week). Most anecdotal reports seem to indicate a faster release with IM, and overall higher levels.
I just use 1/2 27 gauge insulin needles. Lately I have been pinning the sides of my lats, and it is the best spot I have found. Not one painful injection yet. Delts are pretty good, but they hurt for the first month, and I do get an occasional painful shot. You may need a longer needle than I do if you are carrying more fat than I am.