Most F1 Engineers are direct applicants with little or no experience with other teams ( unless swapping between F1 teams ) from what I know. I dont think that there is a clear progression path to F1 from working for smaller teams in the lesser formulae from what I have read.

Not to say there wouldnt be a fulfilling career in working your way up the ranks, but if F1 is a specific goal then I dont think it benefits you trying to do it. I'm sure there's a few peeps on here who've worked in an F1 environment who can help