I'm trying to play more Buttons, but want to do it in such a way that i create a big spr, where i have position and thus can play good poker.

As a sidenote, i use overbets to get a pot growing if i flop or turn a nice hand, but only vs guys who are bad. Or if I suspect a player having a good second best hand.

So, I minraise from the button, what should be my range here so that the sb and bb are indifferent between folding/calling and what should be my 4bet range and size(in relation to their 3bet) be?

How deep are you playing?
Unless you have a very short stack (like for a Spingo), I don't think a complete GTO solution is available for this 3 player game (or even for heads up).

If you're playing 100bb deep in a low rake game against decent opponents (e.g. midstakes+ on Stars), the BB should call the minraise at a very high frequency, due to the sick pot odds. You should probably only open about 45%, because you'll face 3-bets, calls and/or squeezes pretty often. Your minraises clearly won't cause enough folds for steals with ATC to be +EV.

e.g. Assuming you minraise 45% of hands and the SB folds, the BB is at least calling with just over 80% of hands. When you're 100bb deep, the real money is made post-flop. Against weaker opponents (that either fold too much despite the pot odds, or play horribly post), you could try raising 50% or more. (Certainly a few years ago in nitty low stakes Zoom games, some regs were min-opening 80% of BTNs. I don't know if that strat could work today).

Your 4-bet range will depend on the 3b ranges and sizes that the blinds choose, and also the 4-bet size you go with. If the BB raises just over pot with about 11% of hands, you might want to 4-bet pot with 20% of your opening range, and your 4b bluffs will mostly be weak Ax (and Axs) combos that don't do well as calls, or you could go smaller (<20bb) and have fewer bluffs.

I'm sorry for the vague answers, but it's not like I have the complete solution to 6-max poker in my head. No one has access to a precise pre-flop solution to this multiplayer/multi-street game. :/

ah ok, maybe my intention was too greedy.

does a higher size (as a steal and/or 3bet) mean we (should) have more bluffs in our range?

Sort of, but it depends on how deep you are and how your opponent reacts. When you get to (or are on) the river (or are shortstacked, so your "commitment level" is reached sooner), you can bluff more if you use a larger size (or jam) (because bigger sizes force more folds), but the effect is less pronounced pre-flop, because your opponent can still see a flop and play some poker even if you go large.
To some degree, the terms "value bet" and "bluff" don't make perfect sense pre-flop, because every hand has equity. To take an extreme example, you might 3-bet 72o, and refer to it as a 'bluff', but then flop quads. A "bluff" pre-flop can easily turn into a value hand post. (Conversely, you could 3-bet TT for "value", get called by 65s, and be drawing almost dead on 743).
To use a more realistic example, if you're in a tourney with 10bb, you might open jam with something like A2o (and a lot of other hands) in the SB. The shoving range is so wide that you might think you're "bluffing" very often. But if you get called by KQs, you're actually ahead. It's the fact that you're going all in that allows you to jam light and wide. Villain can't "rebluff" if you're already all in.
If you're 3b/4-betting large, but not all in, you don't want to be light too often, because you've giving villain a chance to shove on you. When you're 4-betting, you don't want to go massive if you'll be forced to call a shove with the worst hand. If you choose a very small 4-bet size, then villain will hardly ever fold to it, so you obviously don't want to have many 'bluffs' if you go particularly small. You'd prefer to choose a "happy medium" size that gets enough folds to make your light hands to be profitable, but doesn't lose stacks if villain jams, but also gets called enough by worse to maximise the profit of your best hands. Exactly the optimum size and the balanced range that matches it is something we're all still trying to figure out.

Welcome back arty, we missed you.