insulate concrete garage

Is it nicely dry? You don't want water getting in the joints and then 'pooling' behind the insulation you fit.

Anyways, being 'sectional', does that preclude drilling and plugging in to it? (Are there rebars in there?)

If so, your best solution might be to build a separate, self-supporting studwork frame on the inside, kept slightly away from that wall - use odd little blocks of timber as spacers.

Not sure what the correct construction would then be. I guess it'll be a vapour barrier stapled to the wall side of the framework to protect it, between the frame studs then stuffed with neatly-cut rigid insulation sheets - the best you can afford* - and then ideally overboarding the whole inside with Thermal Laminate Board (plasterboard with insulation layer bonded to it - just the thinnest will do, around 35mm overall thickness) or - to keep costs down - just 'green' plasterboard.

* Jablite will do (it's just a cheap but decent expanded foam material) or Celotex/Kingspan type stuff will be better.

For the floor, if you can get away with a floating type (not nailed or screwed down) that would be best. Is the floor level? I'd just lay down 50mm Jablite (perhaps even glued down with non-solvent tube adhesive) and then float a chipboard T&G floor on top. Use green (waterresistant) chipboard, glues T&Gs.

Ceiling, similar.