Start with proven experience, not the length of the client list. Ask for three or four engagements that match your stack, and then find out whether those engineers are still with the company. An honest provider will introduce you to the tech lead. Vague answers at this stage usually mean the demo work came from somewhere else.
The contract warrants more scrutiny than the proposal. A few clauses carry most of the weight: intellectual property assignment, non-disclosure, and termination and handover. All the work product has to transfer to you on payment, including designs, scripts and infrastructure configuration. Be careful with language that leaves so-called reusable libraries outside the transfer, because it is usually the dependency that makes switching painful.
Ask where their numbers come from. An honest estimate arrives with a written set of assumptions, a breakdown per feature and a best case and why mvps fail a worst case. A fixed-bid deal only makes sense when the specification is complete; in any other case the provider pads the number and you fund the buffer regardless. Time and materials moves the risk back to the client, so it needs a cap, regular demos and transparent reporting.
How the work laravel vs node js which is better run matters more than the number of developers. Find out what happens when the scope changes, who writes the acceptance criteria and what the QA setup looks like. A well-run team should be able to walk you through a working build every one or two weeks. Written acceptance criteria are your only real protection against endless rounds of rework.
Before signing, plan for the handover while the relationship is still good. Ask that the code repository sits on infrastructure you own from the beginning, node vs laravel and that a readme and architecture notes are kept current as the code changes. A partner who is comfortable with this says yes immediately; hesitation here says a great deal.